Vec in alloc::vec - Rust

pub struct Vec<T, A: Allocator = Global> {  }

Expand description

A contiguous growable array type, written as Vec<T>, short for ‘vector’.

§Examples

let mut vec = Vec::new();
vec.push(1);
vec.push(2); assert_eq!(vec.len(), 2);
assert_eq!(vec[0], 1); assert_eq!(vec.pop(), Some(2));
assert_eq!(vec.len(), 1); vec[0] = 7;
assert_eq!(vec[0], 7); vec.extend([1, 2, 3]); for x in &vec { println!("{x}");
}
assert_eq!(vec, [7, 1, 2, 3]);

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The vec! macro is provided for convenient initialization:

let mut vec1 = vec![1, 2, 3];
vec1.push(4);
let vec2 = Vec::from([1, 2, 3, 4]);
assert_eq!(vec1, vec2);

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It can also initialize each element of a Vec<T> with a given value. This may be more efficient than performing allocation and initialization in separate steps, especially when initializing a vector of zeros:

let vec = vec![0; 5];
assert_eq!(vec, [0, 0, 0, 0, 0]); let mut vec = Vec::with_capacity(5);
vec.resize(5, 0);
assert_eq!(vec, [0, 0, 0, 0, 0]);

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For more information, see Capacity and Reallocation.

Use a Vec<T> as an efficient stack:

let mut stack = Vec::new(); stack.push(1);
stack.push(2);
stack.push(3); while let Some(top) = stack.pop() { println!("{top}");
}

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§Indexing

The Vec type allows access to values by index, because it implements the Index trait. An example will be more explicit:

let v = vec![0, 2, 4, 6];
println!("{}", v[1]);

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However be careful: if you try to access an index which isn’t in the Vec, your software will panic! You cannot do this:

ⓘ

let v = vec![0, 2, 4, 6];
println!("{}", v[6]);

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Use get and get_mut if you want to check whether the index is in the Vec.

§Slicing

A Vec can be mutable. On the other hand, slices are read-only objects. To get a slice, use &. Example:

fn read_slice(slice: &[usize]) { } let v = vec![0, 1];
read_slice(&v); let u: &[usize] = &v;
let u: &[_] = &v;

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In Rust, it’s more common to pass slices as arguments rather than vectors when you just want to provide read access. The same goes for String and &str.

§Capacity and reallocation

The capacity of a vector is the amount of space allocated for any future elements that will be added onto the vector. This is not to be confused with the length of a vector, which specifies the number of actual elements within the vector. If a vector’s length exceeds its capacity, its capacity will automatically be increased, but its elements will have to be reallocated.

For example, a vector with capacity 10 and length 0 would be an empty vector with space for 10 more elements. Pushing 10 or fewer elements onto the vector will not change its capacity or cause reallocation to occur. However, if the vector’s length is increased to 11, it will have to reallocate, which can be slow. For this reason, it is recommended to use Vec::with_capacity whenever possible to specify how big the vector is expected to get.

§Guarantees

Due to its incredibly fundamental nature, Vec makes a lot of guarantees about its design. This ensures that it’s as low-overhead as possible in the general case, and can be correctly manipulated in primitive ways by unsafe code. Note that these guarantees refer to an unqualified Vec<T>. If additional type parameters are added (e.g., to support custom allocators), overriding their defaults may change the behavior.

Most fundamentally, Vec is and always will be a (pointer, capacity, length) triplet. No more, no less. The order of these fields is completely unspecified, and you should use the appropriate methods to modify these. The pointer will never be null, so this type is null-pointer-optimized.

However, the pointer might not actually point to allocated memory. In particular, if you construct a Vec with capacity 0 via Vec::new, vec![], Vec::with_capacity(0), or by calling shrink_to_fit on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized types inside a Vec, it will not allocate space for them. Note that in this case the Vec might not report a capacity of 0. Vec will allocate if and only if [mem::size_of::<T>](https://doc.rust-lang.org/1.81.0/core/mem/fn.size_of.html)() * [capacity](struct.Vec.html#method.capacity)() > 0. In general, Vec’s allocation details are very subtle — if you intend to allocate memory using a Vec and use it for something else (either to pass to unsafe code, or to build your own memory-backed collection), be sure to deallocate this memory by using from_raw_parts to recover the Vec and then dropping it.

If a Vec has allocated memory, then the memory it points to is on the heap (as defined by the allocator Rust is configured to use by default), and its pointer points to len initialized, contiguous elements in order (what you would see if you coerced it to a slice), followed by [capacity](struct.Vec.html#method.capacity) - [len](struct.Vec.html#method.len) logically uninitialized, contiguous elements.

A vector containing the elements 'a' and 'b' with capacity 4 can be visualized as below. The top part is the Vec struct, it contains a pointer to the head of the allocation in the heap, length and capacity. The bottom part is the allocation on the heap, a contiguous memory block.

            ptr      len  capacity
       +--------+--------+--------+
       | 0x0123 |      2 |      4 |
       +--------+--------+--------+
            |
            v
Heap   +--------+--------+--------+--------+
       |    'a' |    'b' | uninit | uninit |
       +--------+--------+--------+--------+

uninit represents memory that is not initialized, see MaybeUninit.
Note: the ABI is not stable and Vec makes no guarantees about its memory layout (including the order of fields).

Vec will never perform a “small optimization” where elements are actually stored on the stack for two reasons:

It would make it more difficult for unsafe code to correctly manipulate a Vec. The contents of a Vec wouldn’t have a stable address if it were only moved, and it would be more difficult to determine if a Vec had actually allocated memory.

It would penalize the general case, incurring an additional branch on every access.

Vec will never automatically shrink itself, even if completely empty. This ensures no unnecessary allocations or deallocations occur. Emptying a Vec and then filling it back up to the same len should incur no calls to the allocator. If you wish to free up unused memory, use shrink_to_fit or shrink_to.

push and insert will never (re)allocate if the reported capacity is sufficient. push and insert will (re)allocate if [len](struct.Vec.html#method.len) == [capacity](struct.Vec.html#method.capacity). That is, the reported capacity is completely accurate, and can be relied on. It can even be used to manually free the memory allocated by a Vec if desired. Bulk insertion methods may reallocate, even when not necessary.

Vec does not guarantee any particular growth strategy when reallocating when full, nor when reserve is called. The current strategy is basic and it may prove desirable to use a non-constant growth factor. Whatever strategy is used will of course guarantee O(1) amortized push.

vec![x; n], vec![a, b, c, d], and Vec::with_capacity(n), will all produce a Vec with at least the requested capacity. If [len](struct.Vec.html#method.len) == [capacity](struct.Vec.html#method.capacity), (as is the case for the vec! macro), then a Vec<T> can be converted to and from a Box<[T]> without reallocating or moving the elements.

Vec will not specifically overwrite any data that is removed from it, but also won’t specifically preserve it. Its uninitialized memory is scratch space that it may use however it wants. It will generally just do whatever is most efficient or otherwise easy to implement. Do not rely on removed data to be erased for security purposes. Even if you drop a Vec, its buffer may simply be reused by another allocation. Even if you zero a Vec’s memory first, that might not actually happen because the optimizer does not consider this a side-effect that must be preserved. There is one case which we will not break, however: using unsafe code to write to the excess capacity, and then increasing the length to match, is always valid.

Currently, Vec does not guarantee the order in which elements are dropped. The order has changed in the past and may change again.

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1.0.0 (const: 1.39.0) · source

Constructs a new, empty Vec<T>.

The vector will not allocate until elements are pushed onto it.

§Examples

let mut vec: Vec<i32> = Vec::new();

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1.0.0 · source

Constructs a new, empty Vec<T> with at least the specified capacity.

The vector will be able to hold at least capacity elements without reallocating. This method is allowed to allocate for more elements than capacity. If capacity is 0, the vector will not allocate.

It is important to note that although the returned vector has the minimum capacity specified, the vector will have a zero length. For an explanation of the difference between length and capacity, see Capacity and reallocation.

If it is important to know the exact allocated capacity of a Vec, always use the capacity method after construction.

For Vec<T> where T is a zero-sized type, there will be no allocation and the capacity will always be usize::MAX.

§Panics

Panics if the new capacity exceeds isize::MAX bytes.

§Examples

let mut vec = Vec::with_capacity(10); assert_eq!(vec.len(), 0);
assert!(vec.capacity() >= 10); for i in 0..10 { vec.push(i);
}
assert_eq!(vec.len(), 10);
assert!(vec.capacity() >= 10); vec.push(11);
assert_eq!(vec.len(), 11);
assert!(vec.capacity() >= 11); let vec_units = Vec::<()>::with_capacity(10);
assert_eq!(vec_units.capacity(), usize::MAX);

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source

🔬This is a nightly-only experimental API. (try_with_capacity #91913)

Constructs a new, empty Vec<T> with at least the specified capacity.

§Errors

Returns an error if the capacity exceeds isize::MAX bytes, or if the allocator reports allocation failure.

1.0.0 · source

Creates a Vec<T> directly from a pointer, a length, and a capacity.

§Safety

This is highly unsafe, due to the number of invariants that aren’t checked:

ptr must have been allocated using the global allocator, such as via the alloc::alloc function.
T needs to have the same alignment as what ptr was allocated with. (T having a less strict alignment is not sufficient, the alignment really needs to be equal to satisfy the dealloc requirement that memory must be allocated and deallocated with the same layout.)
The size of T times the capacity (ie. the allocated size in bytes) needs to be the same size as the pointer was allocated with. (Because similar to alignment, dealloc must be called with the same layout size.)
length needs to be less than or equal to capacity.
The first length values must be properly initialized values of type T.
capacity needs to be the capacity that the pointer was allocated with.
The allocated size in bytes must be no larger than isize::MAX. See the safety documentation of pointer::offset.

These requirements are always upheld by any ptr that has been allocated via Vec<T>. Other allocation sources are allowed if the invariants are upheld.

Violating these may cause problems like corrupting the allocator’s internal data structures. For example it is normally not safe to build a Vec<u8> from a pointer to a C char array with length size_t, doing so is only safe if the array was initially allocated by a Vec or String. It’s also not safe to build one from a Vec<u16> and its length, because the allocator cares about the alignment, and these two types have different alignments. The buffer was allocated with alignment 2 (for u16), but after turning it into a Vec<u8> it’ll be deallocated with alignment 1. To avoid these issues, it is often preferable to do casting/transmuting using slice::from_raw_parts instead.

The ownership of ptr is effectively transferred to the Vec<T> which may then deallocate, reallocate or change the contents of memory pointed to by the pointer at will. Ensure that nothing else uses the pointer after calling this function.

§Examples

use std::ptr;
use std::mem; let v = vec![1, 2, 3]; let mut v = mem::ManuallyDrop::new(v); let p = v.as_mut_ptr();
let len = v.len();
let cap = v.capacity(); unsafe { for i in 0..len { ptr::write(p.add(i), 4 + i); } let rebuilt = Vec::from_raw_parts(p, len, cap); assert_eq!(rebuilt, [4, 5, 6]);
}

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Using memory that was allocated elsewhere:

use std::alloc::{alloc, Layout}; fn main() { let layout = Layout::array::<u32>(16).expect("overflow cannot happen"); let vec = unsafe { let mem = alloc(layout).cast::<u32>(); if mem.is_null() { return; } mem.write(1_000_000); Vec::from_raw_parts(mem, 1, 16) }; assert_eq!(vec, &[1_000_000]); assert_eq!(vec.capacity(), 16);
}

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source §

source

🔬This is a nightly-only experimental API. (allocator_api #32838)

Constructs a new, empty Vec<T, A>.

The vector will not allocate until elements are pushed onto it.

§Examples

#![feature(allocator_api)] use std::alloc::System; let mut vec: Vec<i32, _> = Vec::new_in(System);

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source

🔬This is a nightly-only experimental API. (allocator_api #32838)

Constructs a new, empty Vec<T, A> with at least the specified capacity with the provided allocator.

If it is important to know the exact allocated capacity of a Vec, always use the capacity method after construction.

For Vec<T, A> where T is a zero-sized type, there will be no allocation and the capacity will always be usize::MAX.

§Panics

Panics if the new capacity exceeds isize::MAX bytes.

§Examples

#![feature(allocator_api)] use std::alloc::System; let mut vec = Vec::with_capacity_in(10, System); assert_eq!(vec.len(), 0);
assert!(vec.capacity() >= 10); for i in 0..10 { vec.push(i);
}
assert_eq!(vec.len(), 10);
assert!(vec.capacity() >= 10); vec.push(11);
assert_eq!(vec.len(), 11);
assert!(vec.capacity() >= 11); let vec_units = Vec::<(), System>::with_capacity_in(10, System);
assert_eq!(vec_units.capacity(), usize::MAX);

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source

🔬This is a nightly-only experimental API. (allocator_api #32838)

Constructs a new, empty Vec<T, A> with at least the specified capacity with the provided allocator.

§Errors

Returns an error if the capacity exceeds isize::MAX bytes, or if the allocator reports allocation failure.

source

🔬This is a nightly-only experimental API. (allocator_api #32838)

Creates a Vec<T, A> directly from a pointer, a length, a capacity, and an allocator.

§Safety

This is highly unsafe, due to the number of invariants that aren’t checked:

ptr must be currently allocated via the given allocator alloc.
T needs to have the same alignment as what ptr was allocated with. (T having a less strict alignment is not sufficient, the alignment really needs to be equal to satisfy the dealloc requirement that memory must be allocated and deallocated with the same layout.)
The size of T times the capacity (ie. the allocated size in bytes) needs to be the same size as the pointer was allocated with. (Because similar to alignment, dealloc must be called with the same layout size.)
length needs to be less than or equal to capacity.
The first length values must be properly initialized values of type T.
capacity needs to fit the layout size that the pointer was allocated with.
The allocated size in bytes must be no larger than isize::MAX. See the safety documentation of pointer::offset.

These requirements are always upheld by any ptr that has been allocated via Vec<T, A>. Other allocation sources are allowed if the invariants are upheld.

Violating these may cause problems like corrupting the allocator’s internal data structures. For example it is not safe to build a Vec<u8> from a pointer to a C char array with length size_t. It’s also not safe to build one from a Vec<u16> and its length, because the allocator cares about the alignment, and these two types have different alignments. The buffer was allocated with alignment 2 (for u16), but after turning it into a Vec<u8> it’ll be deallocated with alignment 1.

§Examples

#![feature(allocator_api)] use std::alloc::System; use std::ptr;
use std::mem; let mut v = Vec::with_capacity_in(3, System);
v.push(1);
v.push(2);
v.push(3); let mut v = mem::ManuallyDrop::new(v); let p = v.as_mut_ptr();
let len = v.len();
let cap = v.capacity();
let alloc = v.allocator(); unsafe { for i in 0..len { ptr::write(p.add(i), 4 + i); } let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone()); assert_eq!(rebuilt, [4, 5, 6]);
}

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Using memory that was allocated elsewhere:

#![feature(allocator_api)] use std::alloc::{AllocError, Allocator, Global, Layout}; fn main() { let layout = Layout::array::<u32>(16).expect("overflow cannot happen"); let vec = unsafe { let mem = match Global.allocate(layout) { Ok(mem) => mem.cast::<u32>().as_ptr(), Err(AllocError) => return, }; mem.write(1_000_000); Vec::from_raw_parts_in(mem, 1, 16, Global) }; assert_eq!(vec, &[1_000_000]); assert_eq!(vec.capacity(), 16);
}

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source

🔬This is a nightly-only experimental API. (vec_into_raw_parts #65816)

Decomposes a Vec<T> into its raw components: (pointer, length, capacity).

Returns the raw pointer to the underlying data, the length of the vector (in elements), and the allocated capacity of the data (in elements). These are the same arguments in the same order as the arguments to from_raw_parts.

After calling this function, the caller is responsible for the memory previously managed by the Vec. The only way to do this is to convert the raw pointer, length, and capacity back into a Vec with the from_raw_parts function, allowing the destructor to perform the cleanup.

§Examples

#![feature(vec_into_raw_parts)]
let v: Vec<i32> = vec![-1, 0, 1]; let (ptr, len, cap) = v.into_raw_parts(); let rebuilt = unsafe { let ptr = ptr as *mut u32; Vec::from_raw_parts(ptr, len, cap)
};
assert_eq!(rebuilt, [4294967295, 0, 1]);

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source

🔬This is a nightly-only experimental API. (allocator_api #32838)

Decomposes a Vec<T> into its raw components: (pointer, length, capacity, allocator).

Returns the raw pointer to the underlying data, the length of the vector (in elements), the allocated capacity of the data (in elements), and the allocator. These are the same arguments in the same order as the arguments to from_raw_parts_in.

After calling this function, the caller is responsible for the memory previously managed by the Vec. The only way to do this is to convert the raw pointer, length, and capacity back into a Vec with the from_raw_parts_in function, allowing the destructor to perform the cleanup.

§Examples

#![feature(allocator_api, vec_into_raw_parts)] use std::alloc::System; let mut v: Vec<i32, System> = Vec::new_in(System);
v.push(-1);
v.push(0);
v.push(1); let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc(); let rebuilt = unsafe { let ptr = ptr as *mut u32; Vec::from_raw_parts_in(ptr, len, cap, alloc)
};
assert_eq!(rebuilt, [4294967295, 0, 1]);

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1.0.0 · source

Returns the total number of elements the vector can hold without reallocating.

§Examples

let mut vec: Vec<i32> = Vec::with_capacity(10);
vec.push(42);
assert!(vec.capacity() >= 10);

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1.0.0 · source

Reserves capacity for at least additional more elements to be inserted in the given Vec<T>. The collection may reserve more space to speculatively avoid frequent reallocations. After calling reserve, capacity will be greater than or equal to self.len() + additional. Does nothing if capacity is already sufficient.

§Panics

Panics if the new capacity exceeds isize::MAX bytes.

§Examples

let mut vec = vec![1];
vec.reserve(10);
assert!(vec.capacity() >= 11);

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1.0.0 · source

Reserves the minimum capacity for at least additional more elements to be inserted in the given Vec<T>. Unlike reserve, this will not deliberately over-allocate to speculatively avoid frequent allocations. After calling reserve_exact, capacity will be greater than or equal to self.len() + additional. Does nothing if the capacity is already sufficient.

Note that the allocator may give the collection more space than it requests. Therefore, capacity can not be relied upon to be precisely minimal. Prefer reserve if future insertions are expected.

§Panics

Panics if the new capacity exceeds isize::MAX bytes.

§Examples

let mut vec = vec![1];
vec.reserve_exact(10);
assert!(vec.capacity() >= 11);

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1.57.0 · source

Tries to reserve capacity for at least additional more elements to be inserted in the given Vec<T>. The collection may reserve more space to speculatively avoid frequent reallocations. After calling try_reserve, capacity will be greater than or equal to self.len() + additional if it returns Ok(()). Does nothing if capacity is already sufficient. This method preserves the contents even if an error occurs.

§Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

§Examples

use std::collections::TryReserveError; fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> { let mut output = Vec::new(); output.try_reserve(data.len())?; output.extend(data.iter().map(|&val| { val * 2 + 5 })); Ok(output)
}

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1.57.0 · source

Tries to reserve the minimum capacity for at least additional elements to be inserted in the given Vec<T>. Unlike try_reserve, this will not deliberately over-allocate to speculatively avoid frequent allocations. After calling try_reserve_exact, capacity will be greater than or equal to self.len() + additional if it returns Ok(()). Does nothing if the capacity is already sufficient.

Note that the allocator may give the collection more space than it requests. Therefore, capacity can not be relied upon to be precisely minimal. Prefer try_reserve if future insertions are expected.

§Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

§Examples

use std::collections::TryReserveError; fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> { let mut output = Vec::new(); output.try_reserve_exact(data.len())?; output.extend(data.iter().map(|&val| { val * 2 + 5 })); Ok(output)
}

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1.0.0 · source

Shrinks the capacity of the vector as much as possible.

The behavior of this method depends on the allocator, which may either shrink the vector in-place or reallocate. The resulting vector might still have some excess capacity, just as is the case for with_capacity. See Allocator::shrink for more details.

§Examples

let mut vec = Vec::with_capacity(10);
vec.extend([1, 2, 3]);
assert!(vec.capacity() >= 10);
vec.shrink_to_fit();
assert!(vec.capacity() >= 3);

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1.56.0 · source

Shrinks the capacity of the vector with a lower bound.

The capacity will remain at least as large as both the length and the supplied value.

If the current capacity is less than the lower limit, this is a no-op.

§Examples

let mut vec = Vec::with_capacity(10);
vec.extend([1, 2, 3]);
assert!(vec.capacity() >= 10);
vec.shrink_to(4);
assert!(vec.capacity() >= 4);
vec.shrink_to(0);
assert!(vec.capacity() >= 3);

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1.0.0 · source

Converts the vector into Box<[T]>.

Before doing the conversion, this method discards excess capacity like shrink_to_fit.

§Examples

let v = vec![1, 2, 3]; let slice = v.into_boxed_slice();

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Any excess capacity is removed:

let mut vec = Vec::with_capacity(10);
vec.extend([1, 2, 3]); assert!(vec.capacity() >= 10);
let slice = vec.into_boxed_slice();
assert_eq!(slice.into_vec().capacity(), 3);

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1.0.0 · source

Shortens the vector, keeping the first len elements and dropping the rest.

If len is greater or equal to the vector’s current length, this has no effect.

The drain method can emulate truncate, but causes the excess elements to be returned instead of dropped.

Note that this method has no effect on the allocated capacity of the vector.

§Examples

Truncating a five element vector to two elements:

let mut vec = vec![1, 2, 3, 4, 5];
vec.truncate(2);
assert_eq!(vec, [1, 2]);

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No truncation occurs when len is greater than the vector’s current length:

let mut vec = vec![1, 2, 3];
vec.truncate(8);
assert_eq!(vec, [1, 2, 3]);

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Truncating when len == 0 is equivalent to calling the clear method.

let mut vec = vec![1, 2, 3];
vec.truncate(0);
assert_eq!(vec, []);

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1.7.0 · source

Extracts a slice containing the entire vector.

Equivalent to &s[..].

§Examples

use std::io::{self, Write};
let buffer = vec![1, 2, 3, 5, 8];
io::sink().write(buffer.as_slice()).unwrap();

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1.7.0 · source

Extracts a mutable slice of the entire vector.

Equivalent to &mut s[..].

§Examples

use std::io::{self, Read};
let mut buffer = vec![0; 3];
io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();

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1.37.0 · source

Returns a raw pointer to the vector’s buffer, or a dangling raw pointer valid for zero sized reads if the vector didn’t allocate.

The caller must ensure that the vector outlives the pointer this function returns, or else it will end up pointing to garbage. Modifying the vector may cause its buffer to be reallocated, which would also make any pointers to it invalid.

The caller must also ensure that the memory the pointer (non-transitively) points to is never written to (except inside an UnsafeCell) using this pointer or any pointer derived from it. If you need to mutate the contents of the slice, use as_mut_ptr.

This method guarantees that for the purpose of the aliasing model, this method does not materialize a reference to the underlying slice, and thus the returned pointer will remain valid when mixed with other calls to as_ptr and as_mut_ptr. Note that calling other methods that materialize mutable references to the slice, or mutable references to specific elements you are planning on accessing through this pointer, as well as writing to those elements, may still invalidate this pointer. See the second example below for how this guarantee can be used.

§Examples

let x = vec![1, 2, 4];
let x_ptr = x.as_ptr(); unsafe { for i in 0..x.len() { assert_eq!(*x_ptr.add(i), 1 << i);
    }
}

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Due to the aliasing guarantee, the following code is legal:

unsafe { let mut v = vec![0, 1, 2]; let ptr1 = v.as_ptr(); let _ = ptr1.read(); let ptr2 = v.as_mut_ptr().offset(2); ptr2.write(2); let _ = ptr1.read();
}

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1.37.0 · source

Returns an unsafe mutable pointer to the vector’s buffer, or a dangling raw pointer valid for zero sized reads if the vector didn’t allocate.

This method guarantees that for the purpose of the aliasing model, this method does not materialize a reference to the underlying slice, and thus the returned pointer will remain valid when mixed with other calls to as_ptr and as_mut_ptr. Note that calling other methods that materialize references to the slice, or references to specific elements you are planning on accessing through this pointer, may still invalidate this pointer. See the second example below for how this guarantee can be used.

§Examples

let size = 4;
let mut x: Vec<i32> = Vec::with_capacity(size);
let x_ptr = x.as_mut_ptr(); unsafe { for i in 0..size { *x_ptr.add(i) = i as i32; } x.set_len(size);
}
assert_eq!(&*x, &[0, 1, 2, 3]);

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Due to the aliasing guarantee, the following code is legal:

unsafe { let mut v = vec![0]; let ptr1 = v.as_mut_ptr(); ptr1.write(1); let ptr2 = v.as_mut_ptr(); ptr2.write(2); ptr1.write(3);
}

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source

🔬This is a nightly-only experimental API. (allocator_api #32838)

Returns a reference to the underlying allocator.

1.0.0 · source

Forces the length of the vector to new_len.

This is a low-level operation that maintains none of the normal invariants of the type. Normally changing the length of a vector is done using one of the safe operations instead, such as truncate, resize, extend, or clear.

§Safety

new_len must be less than or equal to capacity().
The elements at old_len..new_len must be initialized.

§Examples

This method can be useful for situations in which the vector is serving as a buffer for other code, particularly over FFI:

pub fn get_dictionary(&self) -> Option<Vec<u8>> { let mut dict = Vec::with_capacity(32_768); let mut dict_length = 0; unsafe { let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length); if r == Z_OK { dict.set_len(dict_length); Some(dict) } else { None }
    }
}

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While the following example is sound, there is a memory leak since the inner vectors were not freed prior to the set_len call:

let mut vec = vec![vec![1, 0, 0], vec![0, 1, 0], vec![0, 0, 1]];
unsafe { vec.set_len(0);
}

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Normally, here, one would use clear instead to correctly drop the contents and thus not leak memory.

Removes an element from the vector and returns it.

The removed element is replaced by the last element of the vector.

This does not preserve ordering of the remaining elements, but is O(1). If you need to preserve the element order, use remove instead.

§Panics

Panics if index is out of bounds.

§Examples

let mut v = vec!["foo", "bar", "baz", "qux"]; assert_eq!(v.swap_remove(1), "bar");
assert_eq!(v, ["foo", "qux", "baz"]); assert_eq!(v.swap_remove(0), "foo");
assert_eq!(v, ["baz", "qux"]);

Run

1.0.0 · source

Inserts an element at position index within the vector, shifting all elements after it to the right.

§Panics

Panics if index > len.

§Examples

let mut vec = vec![1, 2, 3];
vec.insert(1, 4);
assert_eq!(vec, [1, 4, 2, 3]);
vec.insert(4, 5);
assert_eq!(vec, [1, 4, 2, 3, 5]);

Run

§Time complexity

Takes O(Vec::len) time. All items after the insertion index must be shifted to the right. In the worst case, all elements are shifted when the insertion index is 0.

Removes and returns the element at position index within the vector, shifting all elements after it to the left.

Note: Because this shifts over the remaining elements, it has a worst-case performance of O(n). If you don’t need the order of elements to be preserved, use swap_remove instead. If you’d like to remove elements from the beginning of the Vec, consider using VecDeque::pop_front instead.

§Panics

Panics if index is out of bounds.

§Examples

let mut v = vec![1, 2, 3];
assert_eq!(v.remove(1), 2);
assert_eq!(v, [1, 3]);

Run

1.0.0 · source

Retains only the elements specified by the predicate.

In other words, remove all elements e for which f(&e) returns false. This method operates in place, visiting each element exactly once in the original order, and preserves the order of the retained elements.

§Examples

let mut vec = vec![1, 2, 3, 4];
vec.retain(|&x| x % 2 == 0);
assert_eq!(vec, [2, 4]);

Run

Because the elements are visited exactly once in the original order, external state may be used to decide which elements to keep.

let mut vec = vec![1, 2, 3, 4, 5];
let keep = [false, true, true, false, true];
let mut iter = keep.iter();
vec.retain(|_| *iter.next().unwrap());
assert_eq!(vec, [2, 3, 5]);

Run

1.61.0 · source

Retains only the elements specified by the predicate, passing a mutable reference to it.

In other words, remove all elements e such that f(&mut e) returns false. This method operates in place, visiting each element exactly once in the original order, and preserves the order of the retained elements.

§Examples

let mut vec = vec![1, 2, 3, 4];
vec.retain_mut(|x| if *x <= 3 { *x += 1; true
} else { false
});
assert_eq!(vec, [2, 3, 4]);

Run

1.16.0 · source

Removes all but the first of consecutive elements in the vector that resolve to the same key.

If the vector is sorted, this removes all duplicates.

§Examples

let mut vec = vec![10, 20, 21, 30, 20]; vec.dedup_by_key(|i| *i / 10); assert_eq!(vec, [10, 20, 30, 20]);

Run

1.16.0 · source

Removes all but the first of consecutive elements in the vector satisfying a given equality relation.

The same_bucket function is passed references to two elements from the vector and must determine if the elements compare equal. The elements are passed in opposite order from their order in the slice, so if same_bucket(a, b) returns true, a is removed.

If the vector is sorted, this removes all duplicates.

§Examples

let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"]; vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b)); assert_eq!(vec, ["foo", "bar", "baz", "bar"]);

Run

1.0.0 · source

Appends an element to the back of a collection.

§Panics

Panics if the new capacity exceeds isize::MAX bytes.

§Examples

let mut vec = vec![1, 2];
vec.push(3);
assert_eq!(vec, [1, 2, 3]);

Run

§Time complexity

Takes amortized O(1) time. If the vector’s length would exceed its capacity after the push, O(capacity) time is taken to copy the vector’s elements to a larger allocation. This expensive operation is offset by the capacity O(1) insertions it allows.

source

🔬This is a nightly-only experimental API. (vec_push_within_capacity #100486)

Appends an element if there is sufficient spare capacity, otherwise an error is returned with the element.

Unlike push this method will not reallocate when there’s insufficient capacity. The caller should use reserve or try_reserve to ensure that there is enough capacity.

§Examples

A manual, panic-free alternative to FromIterator:

#![feature(vec_push_within_capacity)] use std::collections::TryReserveError;
fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> { let mut vec = Vec::new(); for value in iter { if let Err(value) = vec.push_within_capacity(value) { vec.try_reserve(1)?; let _ = vec.push_within_capacity(value); } } Ok(vec)
}
assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));

Run

§Time complexity

Takes O(1) time.

1.0.0 · source

Removes the last element from a vector and returns it, or None if it is empty.

If you’d like to pop the first element, consider using VecDeque::pop_front instead.

§Examples

let mut vec = vec![1, 2, 3];
assert_eq!(vec.pop(), Some(3));
assert_eq!(vec, [1, 2]);

Run

§Time complexity

Takes O(1) time.

source

🔬This is a nightly-only experimental API. (vec_pop_if #122741)

Removes and returns the last element in a vector if the predicate returns true, or None if the predicate returns false or the vector is empty.

§Examples

#![feature(vec_pop_if)] let mut vec = vec![1, 2, 3, 4];
let pred = |x: &mut i32| *x % 2 == 0; assert_eq!(vec.pop_if(pred), Some(4));
assert_eq!(vec, [1, 2, 3]);
assert_eq!(vec.pop_if(pred), None);

Run

1.4.0 · source

Moves all the elements of other into self, leaving other empty.

§Panics

Panics if the new capacity exceeds isize::MAX bytes.

§Examples

let mut vec = vec![1, 2, 3];
let mut vec2 = vec![4, 5, 6];
vec.append(&mut vec2);
assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
assert_eq!(vec2, []);

Run

1.6.0 · source

Removes the specified range from the vector in bulk, returning all removed elements as an iterator. If the iterator is dropped before being fully consumed, it drops the remaining removed elements.

The returned iterator keeps a mutable borrow on the vector to optimize its implementation.

§Panics

Panics if the starting point is greater than the end point or if the end point is greater than the length of the vector.

§Leaking

If the returned iterator goes out of scope without being dropped (due to mem::forget, for example), the vector may have lost and leaked elements arbitrarily, including elements outside the range.

§Examples

let mut v = vec![1, 2, 3];
let u: Vec<_> = v.drain(1..).collect();
assert_eq!(v, &[1]);
assert_eq!(u, &[2, 3]); v.drain(..);
assert_eq!(v, &[]);

Run

1.0.0 · source

Clears the vector, removing all values.

Note that this method has no effect on the allocated capacity of the vector.

§Examples

let mut v = vec![1, 2, 3]; v.clear(); assert!(v.is_empty());

Run

1.0.0 · source

Returns the number of elements in the vector, also referred to as its ‘length’.

§Examples

let a = vec![1, 2, 3];
assert_eq!(a.len(), 3);

Run

1.0.0 · source

Returns true if the vector contains no elements.

§Examples

let mut v = Vec::new();
assert!(v.is_empty()); v.push(1);
assert!(!v.is_empty());

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1.4.0 · source

Splits the collection into two at the given index.

Returns a newly allocated vector containing the elements in the range [at, len). After the call, the original vector will be left containing the elements [0, at) with its previous capacity unchanged.

If you want to take ownership of the entire contents and capacity of the vector, see mem::take or mem::replace.
If you don’t need the returned vector at all, see Vec::truncate.
If you want to take ownership of an arbitrary subslice, or you don’t necessarily want to store the removed items in a vector, see Vec::drain.

§Panics

Panics if at > len.

§Examples

let mut vec = vec![1, 2, 3];
let vec2 = vec.split_off(1);
assert_eq!(vec, [1]);
assert_eq!(vec2, [2, 3]);

Run

1.33.0 · source

Resizes the Vec in-place so that len is equal to new_len.

If new_len is greater than len, the Vec is extended by the difference, with each additional slot filled with the result of calling the closure f. The return values from f will end up in the Vec in the order they have been generated.

If new_len is less than len, the Vec is simply truncated.

This method uses a closure to create new values on every push. If you’d rather Clone a given value, use Vec::resize. If you want to use the Default trait to generate values, you can pass Default::default as the second argument.

§Examples

let mut vec = vec![1, 2, 3];
vec.resize_with(5, Default::default);
assert_eq!(vec, [1, 2, 3, 0, 0]); let mut vec = vec![];
let mut p = 1;
vec.resize_with(4, || { p *= 2; p });
assert_eq!(vec, [2, 4, 8, 16]);

Run

1.47.0 · source

Consumes and leaks the Vec, returning a mutable reference to the contents, &'a mut [T]. Note that the type T must outlive the chosen lifetime 'a. If the type has only static references, or none at all, then this may be chosen to be 'static.

As of Rust 1.57, this method does not reallocate or shrink the Vec, so the leaked allocation may include unused capacity that is not part of the returned slice.

This function is mainly useful for data that lives for the remainder of the program’s life. Dropping the returned reference will cause a memory leak.

§Examples

Simple usage:

let x = vec![1, 2, 3];
let static_ref: &'static mut [usize] = x.leak();
static_ref[0] += 1;
assert_eq!(static_ref, &[2, 2, 3]);

Run

1.60.0 · source

Returns the remaining spare capacity of the vector as a slice of MaybeUninit<T>.

The returned slice can be used to fill the vector with data (e.g. by reading from a file) before marking the data as initialized using the set_len method.

§Examples

let mut v = Vec::with_capacity(10); let uninit = v.spare_capacity_mut();
uninit[0].write(0);
uninit[1].write(1);
uninit[2].write(2); unsafe { v.set_len(3);
} assert_eq!(&v, &[0, 1, 2]);

Run

source

🔬This is a nightly-only experimental API. (vec_split_at_spare #81944)

Returns vector content as a slice of T, along with the remaining spare capacity of the vector as a slice of MaybeUninit<T>.

The returned spare capacity slice can be used to fill the vector with data (e.g. by reading from a file) before marking the data as initialized using the set_len method.

Note that this is a low-level API, which should be used with care for optimization purposes. If you need to append data to a Vec you can use push, extend, extend_from_slice, extend_from_within, insert, append, resize or resize_with, depending on your exact needs.

§Examples

#![feature(vec_split_at_spare)] let mut v = vec![1, 1, 2]; v.reserve(10); let (init, uninit) = v.split_at_spare_mut();
let sum = init.iter().copied().sum::<u32>(); uninit[0].write(sum);
uninit[1].write(sum * 2);
uninit[2].write(sum * 3);
uninit[3].write(sum * 4); unsafe { let len = v.len(); v.set_len(len + 4);
} assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);

Run

source §

1.5.0 · source

Resizes the Vec in-place so that len is equal to new_len.

If new_len is greater than len, the Vec is extended by the difference, with each additional slot filled with value. If new_len is less than len, the Vec is simply truncated.

This method requires T to implement Clone, in order to be able to clone the passed value. If you need more flexibility (or want to rely on Default instead of Clone), use Vec::resize_with. If you only need to resize to a smaller size, use Vec::truncate.

§Examples

let mut vec = vec!["hello"];
vec.resize(3, "world");
assert_eq!(vec, ["hello", "world", "world"]); let mut vec = vec![1, 2, 3, 4];
vec.resize(2, 0);
assert_eq!(vec, [1, 2]);

Run

1.6.0 · source

Clones and appends all elements in a slice to the Vec.

Iterates over the slice other, clones each element, and then appends it to this Vec. The other slice is traversed in-order.

Note that this function is same as extend except that it is specialized to work with slices instead. If and when Rust gets specialization this function will likely be deprecated (but still available).

§Examples

let mut vec = vec![1];
vec.extend_from_slice(&[2, 3, 4]);
assert_eq!(vec, [1, 2, 3, 4]);

Run

1.53.0 · source

Copies elements from src range to the end of the vector.

§Panics

Panics if the starting point is greater than the end point or if the end point is greater than the length of the vector.

§Examples

let mut vec = vec![0, 1, 2, 3, 4]; vec.extend_from_within(2..);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]); vec.extend_from_within(..2);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]); vec.extend_from_within(4..8);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);

Run

source §

1.80.0 · source

Takes a Vec<[T; N]> and flattens it into a Vec<T>.

§Panics

Panics if the length of the resulting vector would overflow a usize.

This is only possible when flattening a vector of arrays of zero-sized types, and thus tends to be irrelevant in practice. If size_of::<T>() > 0, this will never panic.

§Examples

let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
assert_eq!(vec.pop(), Some([7, 8, 9])); let mut flattened = vec.into_flattened();
assert_eq!(flattened.pop(), Some(6));

Run

source §

1.0.0 · source

Removes consecutive repeated elements in the vector according to the PartialEq trait implementation.

If the vector is sorted, this removes all duplicates.

§Examples

let mut vec = vec![1, 2, 2, 3, 2]; vec.dedup(); assert_eq!(vec, [1, 2, 3, 2]);

Run

source §

1.21.0 · source

Creates a splicing iterator that replaces the specified range in the vector with the given replace_with iterator and yields the removed items. replace_with does not need to be the same length as range.

range is removed even if the iterator is not consumed until the end.

It is unspecified how many elements are removed from the vector if the Splice value is leaked.

The input iterator replace_with is only consumed when the Splice value is dropped.

This is optimal if:

The tail (elements in the vector after range) is empty,
or replace_with yields fewer or equal elements than range’s length
or the lower bound of its size_hint() is exact.

Otherwise, a temporary vector is allocated and the tail is moved twice.

§Panics

Panics if the starting point is greater than the end point or if the end point is greater than the length of the vector.

§Examples

let mut v = vec![1, 2, 3, 4];
let new = [7, 8, 9];
let u: Vec<_> = v.splice(1..3, new).collect();
assert_eq!(v, &[1, 7, 8, 9, 4]);
assert_eq!(u, &[2, 3]);

Run

🔬This is a nightly-only experimental API. (extract_if #43244)

Creates an iterator which uses a closure to determine if an element should be removed.

If the closure returns true, then the element is removed and yielded. If the closure returns false, the element will remain in the vector and will not be yielded by the iterator.

If the returned ExtractIf is not exhausted, e.g. because it is dropped without iterating or the iteration short-circuits, then the remaining elements will be retained. Use retain with a negated predicate if you do not need the returned iterator.

Using this method is equivalent to the following code:

let mut i = 0;
while i < vec.len() { if some_predicate(&mut vec[i]) { let val = vec.remove(i); } else { i += 1;
    }
}

Run

But extract_if is easier to use. extract_if is also more efficient, because it can backshift the elements of the array in bulk.

Note that extract_if also lets you mutate every element in the filter closure, regardless of whether you choose to keep or remove it.

§Examples

Splitting an array into evens and odds, reusing the original allocation:

#![feature(extract_if)]
let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15]; let evens = numbers.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
let odds = numbers; assert_eq!(evens, vec![2, 4, 6, 8, 14]);
assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);

Run

1.0.0 · source

Sorts the slice, preserving initial order of equal elements.

This sort is stable (i.e., does not reorder equal elements) and O(n * log(n)) worst-case.

If the implementation of Ord for T does not implement a total order the resulting order of elements in the slice is unspecified. All original elements will remain in the slice and any possible modifications via interior mutability are observed in the input. Same is true if the implementation of Ord for T panics.

When applicable, unstable sorting is preferred because it is generally faster than stable sorting and it doesn’t allocate auxiliary memory. See sort_unstable. The exception are partially sorted slices, which may be better served with slice::sort.

Sorting types that only implement PartialOrd such as f32 and f64 require additional precautions. For example, f32::NAN != f32::NAN, which doesn’t fulfill the reflexivity requirement of Ord. By using an alternative comparison function with slice::sort_by such as f32::total_cmp or f64::total_cmp that defines a total order users can sort slices containing floating-point values. Alternatively, if all values in the slice are guaranteed to be in a subset for which PartialOrd::partial_cmp forms a total order, it’s possible to sort the slice with sort_by(|a, b| a.partial_cmp(b).unwrap()).

§Current implementation

The current implementation is based on driftsort by Orson Peters and Lukas Bergdoll, which combines the fast average case of quicksort with the fast worst case and partial run detection of mergesort, achieving linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the expected time to sort the data is O(n * log(k)).

The auxiliary memory allocation behavior depends on the input length. Short slices are handled without allocation, medium sized slices allocate self.len() and beyond that it clamps at self.len() / 2.

§Panics

May panic if the implementation of Ord for T does not implement a total order.

§Examples

let mut v = [4, -5, 1, -3, 2]; v.sort();
assert_eq!(v, [-5, -3, 1, 2, 4]);

Run

1.0.0 · source

Sorts the slice with a comparison function, preserving initial order of equal elements.

This sort is stable (i.e., does not reorder equal elements) and O(n * log(n)) worst-case.

If the comparison function compare does not implement a total order the resulting order of elements in the slice is unspecified. All original elements will remain in the slice and any possible modifications via interior mutability are observed in the input. Same is true if compare panics.

For example |a, b| (a - b).cmp(a) is a comparison function that is neither transitive nor reflexive nor total, a < b < c < a with a = 1, b = 2, c = 3. For more information and examples see the Ord documentation.

§Current implementation

§Panics

May panic if compare does not implement a total order.

§Examples

let mut v = [4, -5, 1, -3, 2];
v.sort_by(|a, b| a.cmp(b));
assert_eq!(v, [-5, -3, 1, 2, 4]); v.sort_by(|a, b| b.cmp(a));
assert_eq!(v, [4, 2, 1, -3, -5]);

Run

1.7.0 · source

Sorts the slice with a key extraction function, preserving initial order of equal elements.

This sort is stable (i.e., does not reorder equal elements) and O(m * n * log(n)) worst-case, where the key function is O(m).

If the implementation of Ord for K does not implement a total order the resulting order of elements in the slice is unspecified. All original elements will remain in the slice and any possible modifications via interior mutability are observed in the input. Same is true if the implementation of Ord for K panics.

§Current implementation

§Panics

May panic if the implementation of Ord for K does not implement a total order.

§Examples

let mut v = [4i32, -5, 1, -3, 2]; v.sort_by_key(|k| k.abs());
assert_eq!(v, [1, 2, -3, 4, -5]);

Run

1.34.0 · source

Sorts the slice with a key extraction function, preserving initial order of equal elements.

This sort is stable (i.e., does not reorder equal elements) and O(m * n + n * log(n)) worst-case, where the key function is O(m).

During sorting, the key function is called at most once per element, by using temporary storage to remember the results of key evaluation. The order of calls to the key function is unspecified and may change in future versions of the standard library.

For simple key functions (e.g., functions that are property accesses or basic operations), sort_by_key is likely to be faster.

§Current implementation

The current implementation is based on instruction-parallel-network sort by Lukas Bergdoll, which combines the fast average case of randomized quicksort with the fast worst case of heapsort, while achieving linear time on fully sorted and reversed inputs. And O(k * log(n)) where k is the number of distinct elements in the input. It leverages superscalar out-of-order execution capabilities commonly found in CPUs, to efficiently perform the operation.

In the worst case, the algorithm allocates temporary storage in a Vec<(K, usize)> the length of the slice.

§Panics

May panic if the implementation of Ord for K does not implement a total order.

§Examples

let mut v = [4i32, -5, 1, -3, 2, 10]; v.sort_by_cached_key(|k| k.to_string());
assert_eq!(v, [-3, -5, 1, 10, 2, 4]);

Run

1.0.0 · source

Copies self into a new Vec.

§Examples

let s = [10, 40, 30];
let x = s.to_vec();

Run

source

🔬This is a nightly-only experimental API. (allocator_api #32838)

Copies self into a new Vec with an allocator.

§Examples

#![feature(allocator_api)] use std::alloc::System; let s = [10, 40, 30];
let x = s.to_vec_in(System);

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1.40.0 · source

Creates a vector by copying a slice n times.

§Panics

This function will panic if the capacity would overflow.

§Examples

Basic usage:

assert_eq!([1, 2].repeat(3), vec![1, 2, 1, 2, 1, 2]);

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A panic upon overflow:

ⓘ

b"0123456789abcdef".repeat(usize::MAX);

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1.0.0 · source

Flattens a slice of T into a single value Self::Output.

§Examples

assert_eq!(["hello", "world"].concat(), "helloworld");
assert_eq!([[1, 2], [3, 4]].concat(), [1, 2, 3, 4]);

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1.3.0 · source

Flattens a slice of T into a single value Self::Output, placing a given separator between each.

§Examples

assert_eq!(["hello", "world"].join(" "), "hello world");
assert_eq!([[1, 2], [3, 4]].join(&0), [1, 2, 0, 3, 4]);
assert_eq!([[1, 2], [3, 4]].join(&[0, 0][..]), [1, 2, 0, 0, 3, 4]);

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1.0.0 · source

👎Deprecated since 1.3.0: renamed to join

Flattens a slice of T into a single value Self::Output, placing a given separator between each.

§Examples

assert_eq!(["hello", "world"].connect(" "), "hello world");
assert_eq!([[1, 2], [3, 4]].connect(&0), [1, 2, 0, 3, 4]);

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1.23.0 · source

Returns a vector containing a copy of this slice where each byte is mapped to its ASCII upper case equivalent.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To uppercase the value in-place, use make_ascii_uppercase.

1.23.0 · source

Returns a vector containing a copy of this slice where each byte is mapped to its ASCII lower case equivalent.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To lowercase the value in-place, use make_ascii_lowercase.

1.80.0 · source

Takes a &[[T; N]], and flattens it to a &[T].

§Panics

This panics if the length of the resulting slice would overflow a usize.

This is only possible when flattening a slice of arrays of zero-sized types, and thus tends to be irrelevant in practice. If size_of::<T>() > 0, this will never panic.

§Examples

assert_eq!([[1, 2, 3], [4, 5, 6]].as_flattened(), &[1, 2, 3, 4, 5, 6]); assert_eq!( [[1, 2, 3], [4, 5, 6]].as_flattened(), [[1, 2], [3, 4], [5, 6]].as_flattened(),
); let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
assert!(slice_of_empty_arrays.as_flattened().is_empty()); let empty_slice_of_arrays: &[[u32; 10]] = &[];
assert!(empty_slice_of_arrays.as_flattened().is_empty());

Run

1.80.0 · source

Takes a &mut [[T; N]], and flattens it to a &mut [T].

§Panics

This panics if the length of the resulting slice would overflow a usize.

This is only possible when flattening a slice of arrays of zero-sized types, and thus tends to be irrelevant in practice. If size_of::<T>() > 0, this will never panic.

§Examples

fn add_5_to_all(slice: &mut [i32]) { for i in slice { *i += 5; }
} let mut array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
add_5_to_all(array.as_flattened_mut());
assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]);

Run

source

🔬This is a nightly-only experimental API. (sort_floats #93396)

Sorts the slice of floats.

This sort is in-place (i.e. does not allocate), O(n * log(n)) worst-case, and uses the ordering defined by f64::total_cmp.

§Current implementation

This uses the same sorting algorithm as sort_unstable_by.

§Examples

#![feature(sort_floats)]
let mut v = [2.6, -5e-8, f64::NAN, 8.29, f64::INFINITY, -1.0, 0.0, -f64::INFINITY, -0.0]; v.sort_floats();
let sorted = [-f64::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f64::INFINITY, f64::NAN];
assert_eq!(&v[..8], &sorted[..8]);
assert!(v[8].is_nan());

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1.79.0 · source

Creates an iterator over the contiguous valid UTF-8 ranges of this slice, and the non-UTF-8 fragments in between.

§Examples

This function formats arbitrary but mostly-UTF-8 bytes into Rust source code in the form of a C-string literal (c"...").

use std::fmt::Write as _; pub fn cstr_literal(bytes: &[u8]) -> String { let mut repr = String::new(); repr.push_str("c\""); for chunk in bytes.utf8_chunks() { for ch in chunk.valid().chars() { write!(repr, "{}", ch.escape_debug()).unwrap(); } for byte in chunk.invalid() { write!(repr, "\\x{:02X}", byte).unwrap(); } } repr.push('"'); repr
} fn main() { let lit = cstr_literal(b"\xferris the \xf0\x9f\xa6\x80\x07"); let expected = stringify!(c"\xFErris the 🦀\u{7}"); assert_eq!(lit, expected);
}

Run

source

🔬This is a nightly-only experimental API. (ascii_char #110998)

Views this slice of ASCII characters as a UTF-8 str.

source

🔬This is a nightly-only experimental API. (ascii_char #110998)

Views this slice of ASCII characters as a slice of u8 bytes.

source

🔬This is a nightly-only experimental API. (sort_floats #93396)

Sorts the slice of floats.

This sort is in-place (i.e. does not allocate), O(n * log(n)) worst-case, and uses the ordering defined by f32::total_cmp.

§Current implementation

This uses the same sorting algorithm as sort_unstable_by.

§Examples

#![feature(sort_floats)]
let mut v = [2.6, -5e-8, f32::NAN, 8.29, f32::INFINITY, -1.0, 0.0, -f32::INFINITY, -0.0]; v.sort_floats();
let sorted = [-f32::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f32::INFINITY, f32::NAN];
assert_eq!(&v[..8], &sorted[..8]);
assert!(v[8].is_nan());

Run

1.23.0 · source

Checks if all bytes in this slice are within the ASCII range.

source

🔬This is a nightly-only experimental API. (ascii_char #110998)

source

🔬This is a nightly-only experimental API. (ascii_char #110998)

Converts this slice of bytes into a slice of ASCII characters, without checking whether they’re valid.

§Safety

Every byte in the slice must be in 0..=127, or else this is UB.

1.23.0 · source

Checks that two slices are an ASCII case-insensitive match.

Same as to_ascii_lowercase(a) == to_ascii_lowercase(b), but without allocating and copying temporaries.

1.23.0 · source

Converts this slice to its ASCII upper case equivalent in-place.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To return a new uppercased value without modifying the existing one, use to_ascii_uppercase.

1.23.0 · source

Converts this slice to its ASCII lower case equivalent in-place.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To return a new lowercased value without modifying the existing one, use to_ascii_lowercase.

1.60.0 · source

Returns an iterator that produces an escaped version of this slice, treating it as an ASCII string.

§Examples

let s = b"0\t\r\n'\"\\\x9d";
let escaped = s.escape_ascii().to_string();
assert_eq!(escaped, "0\\t\\r\\n\\'\\\"\\\\\\x9d");

Run

1.80.0 · source

Returns a byte slice with leading ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace.

§Examples

assert_eq!(b" \t hello world\n".trim_ascii_start(), b"hello world\n");
assert_eq!(b" ".trim_ascii_start(), b"");
assert_eq!(b"".trim_ascii_start(), b"");

Run

1.80.0 · source

Returns a byte slice with trailing ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace.

§Examples

assert_eq!(b"\r hello world\n ".trim_ascii_end(), b"\r hello world");
assert_eq!(b" ".trim_ascii_end(), b"");
assert_eq!(b"".trim_ascii_end(), b"");

Run

1.80.0 · source

Returns a byte slice with leading and trailing ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace.

§Examples

assert_eq!(b"\r hello world\n ".trim_ascii(), b"hello world");
assert_eq!(b" ".trim_ascii(), b"");
assert_eq!(b"".trim_ascii(), b"");

Run

1.0.0 · source

Returns the number of elements in the slice.

§Examples

let a = [1, 2, 3];
assert_eq!(a.len(), 3);

Run

1.0.0 · source

Returns true if the slice has a length of 0.

§Examples

let a = [1, 2, 3];
assert!(!a.is_empty()); let b: &[i32] = &[];
assert!(b.is_empty());

Run

1.0.0 · source

Returns the first element of the slice, or None if it is empty.

§Examples

let v = [10, 40, 30];
assert_eq!(Some(&10), v.first()); let w: &[i32] = &[];
assert_eq!(None, w.first());

Run

1.0.0 · source

Returns a mutable pointer to the first element of the slice, or None if it is empty.

§Examples

let x = &mut [0, 1, 2]; if let Some(first) = x.first_mut() { *first = 5;
}
assert_eq!(x, &[5, 1, 2]); let y: &mut [i32] = &mut [];
assert_eq!(None, y.first_mut());

Run

1.5.0 · source

Returns the first and all the rest of the elements of the slice, or None if it is empty.

§Examples

let x = &[0, 1, 2]; if let Some((first, elements)) = x.split_first() { assert_eq!(first, &0); assert_eq!(elements, &[1, 2]);
}

Run

1.5.0 · source

Returns the first and all the rest of the elements of the slice, or None if it is empty.

§Examples

let x = &mut [0, 1, 2]; if let Some((first, elements)) = x.split_first_mut() { *first = 3; elements[0] = 4; elements[1] = 5;
}
assert_eq!(x, &[3, 4, 5]);

Run

1.5.0 · source

Returns the last and all the rest of the elements of the slice, or None if it is empty.

§Examples

let x = &[0, 1, 2]; if let Some((last, elements)) = x.split_last() { assert_eq!(last, &2); assert_eq!(elements, &[0, 1]);
}

Run

1.5.0 · source

Returns the last and all the rest of the elements of the slice, or None if it is empty.

§Examples

let x = &mut [0, 1, 2]; if let Some((last, elements)) = x.split_last_mut() { *last = 3; elements[0] = 4; elements[1] = 5;
}
assert_eq!(x, &[4, 5, 3]);

Run

1.0.0 · source

Returns the last element of the slice, or None if it is empty.

§Examples

let v = [10, 40, 30];
assert_eq!(Some(&30), v.last()); let w: &[i32] = &[];
assert_eq!(None, w.last());

Run

1.0.0 · source

Returns a mutable reference to the last item in the slice, or None if it is empty.

§Examples

let x = &mut [0, 1, 2]; if let Some(last) = x.last_mut() { *last = 10;
}
assert_eq!(x, &[0, 1, 10]); let y: &mut [i32] = &mut [];
assert_eq!(None, y.last_mut());

Run

1.77.0 · source

Return an array reference to the first N items in the slice.

If the slice is not at least N in length, this will return None.

§Examples

let u = [10, 40, 30];
assert_eq!(Some(&[10, 40]), u.first_chunk::<2>()); let v: &[i32] = &[10];
assert_eq!(None, v.first_chunk::<2>()); let w: &[i32] = &[];
assert_eq!(Some(&[]), w.first_chunk::<0>());

Run

1.77.0 · source

Return a mutable array reference to the first N items in the slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &mut [0, 1, 2]; if let Some(first) = x.first_chunk_mut::<2>() { first[0] = 5; first[1] = 4;
}
assert_eq!(x, &[5, 4, 2]); assert_eq!(None, x.first_chunk_mut::<4>());

Run

1.77.0 · source

Return an array reference to the first N items in the slice and the remaining slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &[0, 1, 2]; if let Some((first, elements)) = x.split_first_chunk::<2>() { assert_eq!(first, &[0, 1]); assert_eq!(elements, &[2]);
} assert_eq!(None, x.split_first_chunk::<4>());

Run

1.77.0 · source

Return a mutable array reference to the first N items in the slice and the remaining slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &mut [0, 1, 2]; if let Some((first, elements)) = x.split_first_chunk_mut::<2>() { first[0] = 3; first[1] = 4; elements[0] = 5;
}
assert_eq!(x, &[3, 4, 5]); assert_eq!(None, x.split_first_chunk_mut::<4>());

Run

1.77.0 · source

Return an array reference to the last N items in the slice and the remaining slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &[0, 1, 2]; if let Some((elements, last)) = x.split_last_chunk::<2>() { assert_eq!(elements, &[0]); assert_eq!(last, &[1, 2]);
} assert_eq!(None, x.split_last_chunk::<4>());

Run

1.77.0 · source

Return a mutable array reference to the last N items in the slice and the remaining slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &mut [0, 1, 2]; if let Some((elements, last)) = x.split_last_chunk_mut::<2>() { last[0] = 3; last[1] = 4; elements[0] = 5;
}
assert_eq!(x, &[5, 3, 4]); assert_eq!(None, x.split_last_chunk_mut::<4>());

Run

1.77.0 · source

Return an array reference to the last N items in the slice.

If the slice is not at least N in length, this will return None.

§Examples

let u = [10, 40, 30];
assert_eq!(Some(&[40, 30]), u.last_chunk::<2>()); let v: &[i32] = &[10];
assert_eq!(None, v.last_chunk::<2>()); let w: &[i32] = &[];
assert_eq!(Some(&[]), w.last_chunk::<0>());

Run

1.77.0 · source

Return a mutable array reference to the last N items in the slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &mut [0, 1, 2]; if let Some(last) = x.last_chunk_mut::<2>() { last[0] = 10; last[1] = 20;
}
assert_eq!(x, &[0, 10, 20]); assert_eq!(None, x.last_chunk_mut::<4>());

Run

1.0.0 · source

Returns a reference to an element or subslice depending on the type of index.

If given a position, returns a reference to the element at that position or None if out of bounds.
If given a range, returns the subslice corresponding to that range, or None if out of bounds.

§Examples

let v = [10, 40, 30];
assert_eq!(Some(&40), v.get(1));
assert_eq!(Some(&[10, 40][..]), v.get(0..2));
assert_eq!(None, v.get(3));
assert_eq!(None, v.get(0..4));

Run

1.0.0 · source

Returns a mutable reference to an element or subslice depending on the type of index (see get) or None if the index is out of bounds.

§Examples

let x = &mut [0, 1, 2]; if let Some(elem) = x.get_mut(1) { *elem = 42;
}
assert_eq!(x, &[0, 42, 2]);

Run

1.0.0 · source

Returns a reference to an element or subslice, without doing bounds checking.

For a safe alternative see get.

§Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used.

You can think of this like .get(index).unwrap_unchecked(). It’s UB to call .get_unchecked(len), even if you immediately convert to a pointer. And it’s UB to call .get_unchecked(..len + 1), .get_unchecked(..=len), or similar.

§Examples

let x = &[1, 2, 4]; unsafe { assert_eq!(x.get_unchecked(1), &2);
}

Run

1.0.0 · source

Returns a mutable reference to an element or subslice, without doing bounds checking.

For a safe alternative see get_mut.

§Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used.

You can think of this like .get_mut(index).unwrap_unchecked(). It’s UB to call .get_unchecked_mut(len), even if you immediately convert to a pointer. And it’s UB to call .get_unchecked_mut(..len + 1), .get_unchecked_mut(..=len), or similar.

§Examples

let x = &mut [1, 2, 4]; unsafe { let elem = x.get_unchecked_mut(1); *elem = 13;
}
assert_eq!(x, &[1, 13, 4]);

Run

1.0.0 · source

Returns a raw pointer to the slice’s buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up pointing to garbage.

Modifying the container referenced by this slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

§Examples

let x = &[1, 2, 4];
let x_ptr = x.as_ptr(); unsafe { for i in 0..x.len() { assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
    }
}

Run

1.0.0 · source

Returns an unsafe mutable pointer to the slice’s buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up pointing to garbage.

Modifying the container referenced by this slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

§Examples

let x = &mut [1, 2, 4];
let x_ptr = x.as_mut_ptr(); unsafe { for i in 0..x.len() { *x_ptr.add(i) += 2; }
}
assert_eq!(x, &[3, 4, 6]);

Run

1.48.0 · source

Returns the two raw pointers spanning the slice.

The returned range is half-open, which means that the end pointer points one past the last element of the slice. This way, an empty slice is represented by two equal pointers, and the difference between the two pointers represents the size of the slice.

See as_ptr for warnings on using these pointers. The end pointer requires extra caution, as it does not point to a valid element in the slice.

This function is useful for interacting with foreign interfaces which use two pointers to refer to a range of elements in memory, as is common in C++.

It can also be useful to check if a pointer to an element refers to an element of this slice:

let a = [1, 2, 3];
let x = &a[1] as *const _;
let y = &5 as *const _; assert!(a.as_ptr_range().contains(&x));
assert!(!a.as_ptr_range().contains(&y));

Run

1.48.0 · source

Returns the two unsafe mutable pointers spanning the slice.

See as_mut_ptr for warnings on using these pointers. The end pointer requires extra caution, as it does not point to a valid element in the slice.

This function is useful for interacting with foreign interfaces which use two pointers to refer to a range of elements in memory, as is common in C++.

1.0.0 · source

Swaps two elements in the slice.

If a equals to b, it’s guaranteed that elements won’t change value.

§Arguments

a - The index of the first element
b - The index of the second element

§Panics

Panics if a or b are out of bounds.

§Examples

let mut v = ["a", "b", "c", "d", "e"];
v.swap(2, 4);
assert!(v == ["a", "b", "e", "d", "c"]);

Run

source

🔬This is a nightly-only experimental API. (slice_swap_unchecked #88539)

Swaps two elements in the slice, without doing bounds checking.

For a safe alternative see swap.

§Arguments

a - The index of the first element
b - The index of the second element

§Safety

Calling this method with an out-of-bounds index is undefined behavior. The caller has to ensure that a < self.len() and b < self.len().

§Examples

#![feature(slice_swap_unchecked)] let mut v = ["a", "b", "c", "d"];
unsafe { v.swap_unchecked(1, 3) };
assert!(v == ["a", "d", "c", "b"]);

Run

1.0.0 · source

Reverses the order of elements in the slice, in place.

§Examples

let mut v = [1, 2, 3];
v.reverse();
assert!(v == [3, 2, 1]);

Run

1.0.0 · source

Returns an iterator over the slice.

The iterator yields all items from start to end.

§Examples

let x = &[1, 2, 4];
let mut iterator = x.iter(); assert_eq!(iterator.next(), Some(&1));
assert_eq!(iterator.next(), Some(&2));
assert_eq!(iterator.next(), Some(&4));
assert_eq!(iterator.next(), None);

Run

1.0.0 · source

Returns an iterator that allows modifying each value.

The iterator yields all items from start to end.

§Examples

let x = &mut [1, 2, 4];
for elem in x.iter_mut() { *elem += 2;
}
assert_eq!(x, &[3, 4, 6]);

Run

1.0.0 · source

Returns an iterator over all contiguous windows of length size. The windows overlap. If the slice is shorter than size, the iterator returns no values.

§Panics

Panics if size is 0.

§Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.windows(3);
assert_eq!(iter.next().unwrap(), &['l', 'o', 'r']);
assert_eq!(iter.next().unwrap(), &['o', 'r', 'e']);
assert_eq!(iter.next().unwrap(), &['r', 'e', 'm']);
assert!(iter.next().is_none());

Run

If the slice is shorter than size:

let slice = ['f', 'o', 'o'];
let mut iter = slice.windows(4);
assert!(iter.next().is_none());

Run

There’s no windows_mut, as that existing would let safe code violate the “only one &mut at a time to the same thing” rule. However, you can sometimes use Cell::as_slice_of_cells in conjunction with windows to accomplish something similar:

use std::cell::Cell; let mut array = ['R', 'u', 's', 't', ' ', '2', '0', '1', '5'];
let slice = &mut array[..];
let slice_of_cells: &[Cell<char>] = Cell::from_mut(slice).as_slice_of_cells();
for w in slice_of_cells.windows(3) { Cell::swap(&w[0], &w[2]);
}
assert_eq!(array, ['s', 't', ' ', '2', '0', '1', '5', 'u', 'R']);

Run

1.0.0 · source

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are slices and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

See chunks_exact for a variant of this iterator that returns chunks of always exactly chunk_size elements, and rchunks for the same iterator but starting at the end of the slice.

§Panics

Panics if chunk_size is 0.

§Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.chunks(2);
assert_eq!(iter.next().unwrap(), &['l', 'o']);
assert_eq!(iter.next().unwrap(), &['r', 'e']);
assert_eq!(iter.next().unwrap(), &['m']);
assert!(iter.next().is_none());

Run

1.0.0 · source

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

See chunks_exact_mut for a variant of this iterator that returns chunks of always exactly chunk_size elements, and rchunks_mut for the same iterator but starting at the end of the slice.

§Panics

Panics if chunk_size is 0.

§Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1; for chunk in v.chunks_mut(2) { for elem in chunk.iter_mut() { *elem += count; } count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 3]);

Run

1.31.0 · source

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are slices and do not overlap. If chunk_size does not divide the length of the slice, then the last up to chunk_size-1 elements will be omitted and can be retrieved from the remainder function of the iterator.

Due to each chunk having exactly chunk_size elements, the compiler can often optimize the resulting code better than in the case of chunks.

See chunks for a variant of this iterator that also returns the remainder as a smaller chunk, and rchunks_exact for the same iterator but starting at the end of the slice.

§Panics

Panics if chunk_size is 0.

§Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.chunks_exact(2);
assert_eq!(iter.next().unwrap(), &['l', 'o']);
assert_eq!(iter.next().unwrap(), &['r', 'e']);
assert!(iter.next().is_none());
assert_eq!(iter.remainder(), &['m']);

Run

1.31.0 · source

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last up to chunk_size-1 elements will be omitted and can be retrieved from the into_remainder function of the iterator.

Due to each chunk having exactly chunk_size elements, the compiler can often optimize the resulting code better than in the case of chunks_mut.

See chunks_mut for a variant of this iterator that also returns the remainder as a smaller chunk, and rchunks_exact_mut for the same iterator but starting at the end of the slice.

§Panics

Panics if chunk_size is 0.

§Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1; for chunk in v.chunks_exact_mut(2) { for elem in chunk.iter_mut() { *elem += count; } count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 0]);

Run

source

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, assuming that there’s no remainder.

§Safety

This may only be called when

The slice splits exactly into N-element chunks (aka self.len() % N == 0).
N != 0.

§Examples

#![feature(slice_as_chunks)]
let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
let chunks: &[[char; 1]] = unsafe { slice.as_chunks_unchecked() };
assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
let chunks: &[[char; 3]] = unsafe { slice.as_chunks_unchecked() };
assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);

Run

source

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, starting at the beginning of the slice, and a remainder slice with length strictly less than N.

§Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

§Examples

#![feature(slice_as_chunks)]
let slice = ['l', 'o', 'r', 'e', 'm'];
let (chunks, remainder) = slice.as_chunks();
assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
assert_eq!(remainder, &['m']);

Run

If you expect the slice to be an exact multiple, you can combine let-else with an empty slice pattern:

#![feature(slice_as_chunks)]
let slice = ['R', 'u', 's', 't'];
let (chunks, []) = slice.as_chunks::<2>() else { panic!("slice didn't have even length")
};
assert_eq!(chunks, &[['R', 'u'], ['s', 't']]);

Run

source

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, starting at the end of the slice, and a remainder slice with length strictly less than N.

§Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

§Examples

#![feature(slice_as_chunks)]
let slice = ['l', 'o', 'r', 'e', 'm'];
let (remainder, chunks) = slice.as_rchunks();
assert_eq!(remainder, &['l']);
assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);

Run

source

🔬This is a nightly-only experimental API. (array_chunks #74985)

Returns an iterator over N elements of the slice at a time, starting at the beginning of the slice.

The chunks are array references and do not overlap. If N does not divide the length of the slice, then the last up to N-1 elements will be omitted and can be retrieved from the remainder function of the iterator.

This method is the const generic equivalent of chunks_exact.

§Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

§Examples

#![feature(array_chunks)]
let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.array_chunks();
assert_eq!(iter.next().unwrap(), &['l', 'o']);
assert_eq!(iter.next().unwrap(), &['r', 'e']);
assert!(iter.next().is_none());
assert_eq!(iter.remainder(), &['m']);

Run

source

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, assuming that there’s no remainder.

§Safety

This may only be called when

The slice splits exactly into N-element chunks (aka self.len() % N == 0).
N != 0.

§Examples

#![feature(slice_as_chunks)]
let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
let chunks: &mut [[char; 1]] = unsafe { slice.as_chunks_unchecked_mut() };
chunks[0] = ['L'];
assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
let chunks: &mut [[char; 3]] = unsafe { slice.as_chunks_unchecked_mut() };
chunks[1] = ['a', 'x', '?'];
assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);

Run

source

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, starting at the beginning of the slice, and a remainder slice with length strictly less than N.

§Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

§Examples

#![feature(slice_as_chunks)]
let v = &mut [0, 0, 0, 0, 0];
let mut count = 1; let (chunks, remainder) = v.as_chunks_mut();
remainder[0] = 9;
for chunk in chunks { *chunk = [count; 2]; count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 9]);

Run

source

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, starting at the end of the slice, and a remainder slice with length strictly less than N.

§Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

§Examples

#![feature(slice_as_chunks)]
let v = &mut [0, 0, 0, 0, 0];
let mut count = 1; let (remainder, chunks) = v.as_rchunks_mut();
remainder[0] = 9;
for chunk in chunks { *chunk = [count; 2]; count += 1;
}
assert_eq!(v, &[9, 1, 1, 2, 2]);

Run

source

🔬This is a nightly-only experimental API. (array_chunks #74985)

Returns an iterator over N elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable array references and do not overlap. If N does not divide the length of the slice, then the last up to N-1 elements will be omitted and can be retrieved from the into_remainder function of the iterator.

This method is the const generic equivalent of chunks_exact_mut.

§Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

§Examples

#![feature(array_chunks)]
let v = &mut [0, 0, 0, 0, 0];
let mut count = 1; for chunk in v.array_chunks_mut() { *chunk = [count; 2]; count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 0]);

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1; for chunk in v.rchunks_exact_mut(2) { for elem in chunk.iter_mut() { *elem += count; } count += 1;
}
assert_eq!(v, &[0, 2, 2, 1, 1]);

Run

1.77.0 · source

Returns an iterator over the slice producing non-overlapping runs of elements using the predicate to separate them.

The predicate is called for every pair of consecutive elements, meaning that it is called on slice[0] and slice[1], followed by slice[1] and slice[2], and so on.

§Examples

let slice = &[1, 1, 1, 3, 3, 2, 2, 2]; let mut iter = slice.chunk_by(|a, b| a == b); assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
assert_eq!(iter.next(), Some(&[3, 3][..]));
assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
assert_eq!(iter.next(), None);

Run

This method can be used to extract the sorted subslices:

let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4]; let mut iter = slice.chunk_by(|a, b| a <= b); assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
assert_eq!(iter.next(), Some(&[2, 3][..]));
assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
assert_eq!(iter.next(), None);

Run

1.77.0 · source

Returns an iterator over the slice producing non-overlapping mutable runs of elements using the predicate to separate them.

The predicate is called for every pair of consecutive elements, meaning that it is called on slice[0] and slice[1], followed by slice[1] and slice[2], and so on.

§Examples

let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2]; let mut iter = slice.chunk_by_mut(|a, b| a == b); assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
assert_eq!(iter.next(), Some(&mut [3, 3][..]));
assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
assert_eq!(iter.next(), None);

Run

This method can be used to extract the sorted subslices:

let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4]; let mut iter = slice.chunk_by_mut(|a, b| a <= b); assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
assert_eq!(iter.next(), Some(&mut [2, 3][..]));
assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
assert_eq!(iter.next(), None);

Run

1.0.0 · source

Divides one slice into two at an index.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

§Panics

Panics if mid > len. For a non-panicking alternative see split_at_checked.

§Examples

let v = [1, 2, 3, 4, 5, 6]; { let (left, right) = v.split_at(0); assert_eq!(left, []); assert_eq!(right, [1, 2, 3, 4, 5, 6]);
} { let (left, right) = v.split_at(2); assert_eq!(left, [1, 2]); assert_eq!(right, [3, 4, 5, 6]);
} { let (left, right) = v.split_at(6); assert_eq!(left, [1, 2, 3, 4, 5, 6]); assert_eq!(right, []);
}

Run

1.0.0 · source

Divides one mutable slice into two at an index.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

§Panics

Panics if mid > len. For a non-panicking alternative see split_at_mut_checked.

§Examples

let mut v = [1, 0, 3, 0, 5, 6];
let (left, right) = v.split_at_mut(2);
assert_eq!(left, [1, 0]);
assert_eq!(right, [3, 0, 5, 6]);
left[1] = 2;
right[1] = 4;
assert_eq!(v, [1, 2, 3, 4, 5, 6]);

Run

1.79.0 · source

Divides one slice into two at an index, without doing bounds checking.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

For a safe alternative see split_at.

§Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used. The caller has to ensure that 0 <= mid <= self.len().

§Examples

let v = [1, 2, 3, 4, 5, 6]; unsafe { let (left, right) = v.split_at_unchecked(0); assert_eq!(left, []); assert_eq!(right, [1, 2, 3, 4, 5, 6]);
} unsafe { let (left, right) = v.split_at_unchecked(2); assert_eq!(left, [1, 2]); assert_eq!(right, [3, 4, 5, 6]);
} unsafe { let (left, right) = v.split_at_unchecked(6); assert_eq!(left, [1, 2, 3, 4, 5, 6]); assert_eq!(right, []);
}

Run

1.79.0 · source

Divides one mutable slice into two at an index, without doing bounds checking.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

For a safe alternative see split_at_mut.

§Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used. The caller has to ensure that 0 <= mid <= self.len().

§Examples

let mut v = [1, 0, 3, 0, 5, 6];
unsafe { let (left, right) = v.split_at_mut_unchecked(2); assert_eq!(left, [1, 0]); assert_eq!(right, [3, 0, 5, 6]); left[1] = 2; right[1] = 4;
}
assert_eq!(v, [1, 2, 3, 4, 5, 6]);

Run

1.80.0 · source

Divides one slice into two at an index, returning None if the slice is too short.

If mid ≤ len returns a pair of slices where the first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

Otherwise, if mid > len, returns None.

§Examples

let v = [1, -2, 3, -4, 5, -6]; { let (left, right) = v.split_at_checked(0).unwrap(); assert_eq!(left, []); assert_eq!(right, [1, -2, 3, -4, 5, -6]);
} { let (left, right) = v.split_at_checked(2).unwrap(); assert_eq!(left, [1, -2]); assert_eq!(right, [3, -4, 5, -6]);
} { let (left, right) = v.split_at_checked(6).unwrap(); assert_eq!(left, [1, -2, 3, -4, 5, -6]); assert_eq!(right, []);
} assert_eq!(None, v.split_at_checked(7));

Run

1.80.0 · source

Divides one mutable slice into two at an index, returning None if the slice is too short.

Otherwise, if mid > len, returns None.

§Examples

let mut v = [1, 0, 3, 0, 5, 6]; if let Some((left, right)) = v.split_at_mut_checked(2) { assert_eq!(left, [1, 0]); assert_eq!(right, [3, 0, 5, 6]); left[1] = 2; right[1] = 4;
}
assert_eq!(v, [1, 2, 3, 4, 5, 6]); assert_eq!(None, v.split_at_mut_checked(7));

Run

1.0.0 · source

Returns an iterator over subslices separated by elements that match pred. The matched element is not contained in the subslices.

§Examples

let slice = [10, 40, 33, 20];
let mut iter = slice.split(|num| num % 3 == 0); assert_eq!(iter.next().unwrap(), &[10, 40]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

Run

If the first element is matched, an empty slice will be the first item returned by the iterator. Similarly, if the last element in the slice is matched, an empty slice will be the last item returned by the iterator:

let slice = [10, 40, 33];
let mut iter = slice.split(|num| num % 3 == 0); assert_eq!(iter.next().unwrap(), &[10, 40]);
assert_eq!(iter.next().unwrap(), &[]);
assert!(iter.next().is_none());

Run

If two matched elements are directly adjacent, an empty slice will be present between them:

let slice = [10, 6, 33, 20];
let mut iter = slice.split(|num| num % 3 == 0); assert_eq!(iter.next().unwrap(), &[10]);
assert_eq!(iter.next().unwrap(), &[]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

Run

1.0.0 · source

Returns an iterator over mutable subslices separated by elements that match pred. The matched element is not contained in the subslices.

§Examples

let mut v = [10, 40, 30, 20, 60, 50]; for group in v.split_mut(|num| *num % 3 == 0) { group[0] = 1;
}
assert_eq!(v, [1, 40, 30, 1, 60, 1]);

Run

1.51.0 · source

Returns an iterator over subslices separated by elements that match pred. The matched element is contained in the end of the previous subslice as a terminator.

§Examples

let slice = [10, 40, 33, 20];
let mut iter = slice.split_inclusive(|num| num % 3 == 0); assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

Run

If the last element of the slice is matched, that element will be considered the terminator of the preceding slice. That slice will be the last item returned by the iterator.

let slice = [3, 10, 40, 33];
let mut iter = slice.split_inclusive(|num| num % 3 == 0); assert_eq!(iter.next().unwrap(), &[3]);
assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
assert!(iter.next().is_none());

Run

1.51.0 · source

Returns an iterator over mutable subslices separated by elements that match pred. The matched element is contained in the previous subslice as a terminator.

§Examples

let mut v = [10, 40, 30, 20, 60, 50]; for group in v.split_inclusive_mut(|num| *num % 3 == 0) { let terminator_idx = group.len()-1; group[terminator_idx] = 1;
}
assert_eq!(v, [10, 40, 1, 20, 1, 1]);

Run

1.27.0 · source

Returns an iterator over subslices separated by elements that match pred, starting at the end of the slice and working backwards. The matched element is not contained in the subslices.

§Examples

let slice = [11, 22, 33, 0, 44, 55];
let mut iter = slice.rsplit(|num| *num == 0); assert_eq!(iter.next().unwrap(), &[44, 55]);
assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
assert_eq!(iter.next(), None);

Run

As with split(), if the first or last element is matched, an empty slice will be the first (or last) item returned by the iterator.

let v = &[0, 1, 1, 2, 3, 5, 8];
let mut it = v.rsplit(|n| *n % 2 == 0);
assert_eq!(it.next().unwrap(), &[]);
assert_eq!(it.next().unwrap(), &[3, 5]);
assert_eq!(it.next().unwrap(), &[1, 1]);
assert_eq!(it.next().unwrap(), &[]);
assert_eq!(it.next(), None);

Run

1.27.0 · source

Returns an iterator over mutable subslices separated by elements that match pred, starting at the end of the slice and working backwards. The matched element is not contained in the subslices.

§Examples

let mut v = [100, 400, 300, 200, 600, 500]; let mut count = 0;
for group in v.rsplit_mut(|num| *num % 3 == 0) { count += 1; group[0] = count;
}
assert_eq!(v, [3, 400, 300, 2, 600, 1]);

Run

1.0.0 · source

Returns an iterator over subslices separated by elements that match pred, limited to returning at most n items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

§Examples

Print the slice split once by numbers divisible by 3 (i.e., [10, 40], [20, 60, 50]):

let v = [10, 40, 30, 20, 60, 50]; for group in v.splitn(2, |num| *num % 3 == 0) { println!("{group:?}");
}

Run

1.0.0 · source

Returns an iterator over mutable subslices separated by elements that match pred, limited to returning at most n items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

§Examples

let mut v = [10, 40, 30, 20, 60, 50]; for group in v.splitn_mut(2, |num| *num % 3 == 0) { group[0] = 1;
}
assert_eq!(v, [1, 40, 30, 1, 60, 50]);

Run

1.0.0 · source

Returns an iterator over subslices separated by elements that match pred limited to returning at most n items. This starts at the end of the slice and works backwards. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

§Examples

Print the slice split once, starting from the end, by numbers divisible by 3 (i.e., [50], [10, 40, 30, 20]):

let v = [10, 40, 30, 20, 60, 50]; for group in v.rsplitn(2, |num| *num % 3 == 0) { println!("{group:?}");
}

Run

1.0.0 · source

The last element returned, if any, will contain the remainder of the slice.

§Examples

let mut s = [10, 40, 30, 20, 60, 50]; for group in s.rsplitn_mut(2, |num| *num % 3 == 0) { group[0] = 1;
}
assert_eq!(s, [1, 40, 30, 20, 60, 1]);

Run

source

🔬This is a nightly-only experimental API. (slice_split_once #112811)

Splits the slice on the first element that matches the specified predicate.

If any matching elements are present in the slice, returns the prefix before the match and suffix after. The matching element itself is not included. If no elements match, returns None.

§Examples

#![feature(slice_split_once)]
let s = [1, 2, 3, 2, 4];
assert_eq!(s.split_once(|&x| x == 2), Some(( &[1][..], &[3, 2, 4][..]
)));
assert_eq!(s.split_once(|&x| x == 0), None);

Run

source

🔬This is a nightly-only experimental API. (slice_split_once #112811)

Splits the slice on the last element that matches the specified predicate.

If any matching elements are present in the slice, returns the prefix before the match and suffix after. The matching element itself is not included. If no elements match, returns None.

§Examples

#![feature(slice_split_once)]
let s = [1, 2, 3, 2, 4];
assert_eq!(s.rsplit_once(|&x| x == 2), Some(( &[1, 2, 3][..], &[4][..]
)));
assert_eq!(s.rsplit_once(|&x| x == 0), None);

Run

1.0.0 · source

Returns true if the slice contains an element with the given value.

This operation is O(n).

Note that if you have a sorted slice, binary_search may be faster.

§Examples

let v = [10, 40, 30];
assert!(v.contains(&30));
assert!(!v.contains(&50));

Run

If you do not have a &T, but some other value that you can compare with one (for example, String implements PartialEq<str>), you can use iter().any:

let v = [String::from("hello"), String::from("world")]; assert!(v.iter().any(|e| e == "hello")); assert!(!v.iter().any(|e| e == "hi"));

Run

1.0.0 · source

Returns true if needle is a prefix of the slice or equal to the slice.

§Examples

let v = [10, 40, 30];
assert!(v.starts_with(&[10]));
assert!(v.starts_with(&[10, 40]));
assert!(v.starts_with(&v));
assert!(!v.starts_with(&[50]));
assert!(!v.starts_with(&[10, 50]));

Run

Always returns true if needle is an empty slice:

let v = &[10, 40, 30];
assert!(v.starts_with(&[]));
let v: &[u8] = &[];
assert!(v.starts_with(&[]));

Run

1.0.0 · source

Returns true if needle is a suffix of the slice or equal to the slice.

§Examples

let v = [10, 40, 30];
assert!(v.ends_with(&[30]));
assert!(v.ends_with(&[40, 30]));
assert!(v.ends_with(&v));
assert!(!v.ends_with(&[50]));
assert!(!v.ends_with(&[50, 30]));

Run

Always returns true if needle is an empty slice:

let v = &[10, 40, 30];
assert!(v.ends_with(&[]));
let v: &[u8] = &[];
assert!(v.ends_with(&[]));

Run

1.51.0 · source

Returns a subslice with the prefix removed.

If the slice starts with prefix, returns the subslice after the prefix, wrapped in Some. If prefix is empty, simply returns the original slice. If prefix is equal to the original slice, returns an empty slice.

If the slice does not start with prefix, returns None.

§Examples

let v = &[10, 40, 30];
assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
assert_eq!(v.strip_prefix(&[10, 40, 30]), Some(&[][..]));
assert_eq!(v.strip_prefix(&[50]), None);
assert_eq!(v.strip_prefix(&[10, 50]), None); let prefix : &str = "he";
assert_eq!(b"hello".strip_prefix(prefix.as_bytes()), Some(b"llo".as_ref()));

Run

1.51.0 · source

Returns a subslice with the suffix removed.

If the slice ends with suffix, returns the subslice before the suffix, wrapped in Some. If suffix is empty, simply returns the original slice. If suffix is equal to the original slice, returns an empty slice.

If the slice does not end with suffix, returns None.

§Examples

let v = &[10, 40, 30];
assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
assert_eq!(v.strip_suffix(&[10, 40, 30]), Some(&[][..]));
assert_eq!(v.strip_suffix(&[50]), None);
assert_eq!(v.strip_suffix(&[50, 30]), None);

Run

1.0.0 · source

Binary searches this slice for a given element. If the slice is not sorted, the returned result is unspecified and meaningless.

If the value is found then Result::Ok is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then Result::Err is returned, containing the index where a matching element could be inserted while maintaining sorted order.

§Examples

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]; assert_eq!(s.binary_search(&13), Ok(9));
assert_eq!(s.binary_search(&4), Err(7));
assert_eq!(s.binary_search(&100), Err(13));
let r = s.binary_search(&1);
assert!(match r { Ok(1..=4) => true, _ => false, });

Run

If you want to find that whole range of matching items, rather than an arbitrary matching one, that can be done using partition_point:

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]; let low = s.partition_point(|x| x < &1);
assert_eq!(low, 1);
let high = s.partition_point(|x| x <= &1);
assert_eq!(high, 5);
let r = s.binary_search(&1);
assert!((low..high).contains(&r.unwrap())); assert!(s[..low].iter().all(|&x| x < 1));
assert!(s[low..high].iter().all(|&x| x == 1));
assert!(s[high..].iter().all(|&x| x > 1)); assert_eq!(s.partition_point(|x| x < &11), 9);
assert_eq!(s.partition_point(|x| x <= &11), 9);
assert_eq!(s.binary_search(&11), Err(9));

Run

If you want to insert an item to a sorted vector, while maintaining sort order, consider using partition_point:

let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
let num = 42;
let idx = s.partition_point(|&x| x <= num);
s.insert(idx, num);
assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);

Run

1.0.0 · source

Binary searches this slice with a comparator function.

The comparator function should return an order code that indicates whether its argument is Less, Equal or Greater the desired target. If the slice is not sorted or if the comparator function does not implement an order consistent with the sort order of the underlying slice, the returned result is unspecified and meaningless.

§Examples

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]; let seek = 13;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
let seek = 4;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
let seek = 100;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
let seek = 1;
let r = s.binary_search_by(|probe| probe.cmp(&seek));
assert!(match r { Ok(1..=4) => true, _ => false, });

Run

1.10.0 · source

Binary searches this slice with a key extraction function.

Assumes that the slice is sorted by the key, for instance with sort_by_key using the same key extraction function. If the slice is not sorted by the key, the returned result is unspecified and meaningless.

§Examples

Looks up a series of four elements in a slice of pairs sorted by their second elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1), (1, 2), (2, 3), (4, 5), (5, 8), (3, 13), (1, 21), (2, 34), (4, 55)]; assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
let r = s.binary_search_by_key(&1, |&(a, b)| b);
assert!(match r { Ok(1..=4) => true, _ => false, });

Run

1.20.0 · source

Sorts the slice without preserving the initial order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(n * log(n)) worst-case.

Sorting types that only implement PartialOrd such as f32 and f64 require additional precautions. For example, f32::NAN != f32::NAN, which doesn’t fulfill the reflexivity requirement of Ord. By using an alternative comparison function with slice::sort_unstable_by such as f32::total_cmp or f64::total_cmp that defines a total order users can sort slices containing floating-point values. Alternatively, if all values in the slice are guaranteed to be in a subset for which PartialOrd::partial_cmp forms a total order, it’s possible to sort the slice with sort_unstable_by(|a, b| a.partial_cmp(b).unwrap()).

§Current implementation

The current implementation is based on ipnsort by Lukas Bergdoll and Orson Peters, which combines the fast average case of quicksort with the fast worst case of heapsort, achieving linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the expected time to sort the data is O(n * log(k)).

It is typically faster than stable sorting, except in a few special cases, e.g., when the slice is partially sorted.

§Panics

May panic if the implementation of Ord for T does not implement a total order.

§Examples

let mut v = [4, -5, 1, -3, 2]; v.sort_unstable();
assert_eq!(v, [-5, -3, 1, 2, 4]);

Run

1.20.0 · source

Sorts the slice with a comparison function, without preserving the initial order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(n * log(n)) worst-case.

§Current implementation

It is typically faster than stable sorting, except in a few special cases, e.g., when the slice is partially sorted.

§Panics

May panic if compare does not implement a total order.

§Examples

let mut v = [4, -5, 1, -3, 2];
v.sort_unstable_by(|a, b| a.cmp(b));
assert_eq!(v, [-5, -3, 1, 2, 4]); v.sort_unstable_by(|a, b| b.cmp(a));
assert_eq!(v, [4, 2, 1, -3, -5]);

Run

1.20.0 · source

Sorts the slice with a key extraction function, without preserving the initial order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(n * log(n)) worst-case.

§Current implementation

It is typically faster than stable sorting, except in a few special cases, e.g., when the slice is partially sorted.

§Panics

May panic if the implementation of Ord for K does not implement a total order.

§Examples

let mut v = [4i32, -5, 1, -3, 2]; v.sort_unstable_by_key(|k| k.abs());
assert_eq!(v, [1, 2, -3, 4, -5]);

Run

1.49.0 · source

Reorder the slice such that the element at index after the reordering is at its final sorted position.

This reordering has the additional property that any value at position i < index will be less than or equal to any value at a position j > index. Additionally, this reordering is unstable (i.e. any number of equal elements may end up at position index), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

It returns a triplet of the following from the reordered slice: the subslice prior to index, the element at index, and the subslice after index; accordingly, the values in those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to the value of the element at index.

§Current implementation

The current algorithm is an introselect implementation based on ipnsort by Lukas Bergdoll and Orson Peters, which is also the basis for sort_unstable. The fallback algorithm is Median of Medians using Tukey’s Ninther for pivot selection, which guarantees linear runtime for all inputs.

§Panics

Panics when index >= len(), meaning it always panics on empty slices.

May panic if the implementation of Ord for T does not implement a total order.

§Examples

let mut v = [-5i32, 4, 2, -3, 1]; let (lesser, median, greater) = v.select_nth_unstable(2); assert!(lesser == [-3, -5] || lesser == [-5, -3]);
assert_eq!(median, &mut 1);
assert!(greater == [4, 2] || greater == [2, 4]); assert!(v == [-3, -5, 1, 2, 4] || v == [-5, -3, 1, 2, 4] || v == [-3, -5, 1, 4, 2] || v == [-5, -3, 1, 4, 2]);

Run

1.49.0 · source

Reorder the slice with a comparator function such that the element at index after the reordering is at its final sorted position.

This reordering has the additional property that any value at position i < index will be less than or equal to any value at a position j > index using the comparator function. Additionally, this reordering is unstable (i.e. any number of equal elements may end up at position index), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

It returns a triplet of the following from the slice reordered according to the provided comparator function: the subslice prior to index, the element at index, and the subslice after index; accordingly, the values in those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to the value of the element at index.

§Current implementation

§Panics

Panics when index >= len(), meaning it always panics on empty slices.

May panic if compare does not implement a total order.

§Examples

let mut v = [-5i32, 4, 2, -3, 1]; let (lesser, median, greater) = v.select_nth_unstable_by(2, |a, b| b.cmp(a)); assert!(lesser == [4, 2] || lesser == [2, 4]);
assert_eq!(median, &mut 1);
assert!(greater == [-3, -5] || greater == [-5, -3]); assert!(v == [2, 4, 1, -5, -3] || v == [2, 4, 1, -3, -5] || v == [4, 2, 1, -5, -3] || v == [4, 2, 1, -3, -5]);

Run

1.49.0 · source

Reorder the slice with a key extraction function such that the element at index after the reordering is at its final sorted position.

This reordering has the additional property that any value at position i < index will be less than or equal to any value at a position j > index using the key extraction function. Additionally, this reordering is unstable (i.e. any number of equal elements may end up at position index), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

It returns a triplet of the following from the slice reordered according to the provided key extraction function: the subslice prior to index, the element at index, and the subslice after index; accordingly, the values in those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to the value of the element at index.

§Current implementation

§Panics

Panics when index >= len(), meaning it always panics on empty slices.

May panic if K: Ord does not implement a total order.

§Examples

let mut v = [-5i32, 4, 1, -3, 2]; let (lesser, median, greater) = v.select_nth_unstable_by_key(2, |a| a.abs()); assert!(lesser == [1, 2] || lesser == [2, 1]);
assert_eq!(median, &mut -3);
assert!(greater == [4, -5] || greater == [-5, 4]); assert!(v == [1, 2, -3, 4, -5] || v == [1, 2, -3, -5, 4] || v == [2, 1, -3, 4, -5] || v == [2, 1, -3, -5, 4]);

Run

source

🔬This is a nightly-only experimental API. (slice_partition_dedup #54279)

Moves all consecutive repeated elements to the end of the slice according to the PartialEq trait implementation.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

If the slice is sorted, the first returned slice contains no duplicates.

§Examples

#![feature(slice_partition_dedup)] let mut slice = [1, 2, 2, 3, 3, 2, 1, 1]; let (dedup, duplicates) = slice.partition_dedup(); assert_eq!(dedup, [1, 2, 3, 2, 1]);
assert_eq!(duplicates, [2, 3, 1]);

Run

source

🔬This is a nightly-only experimental API. (slice_partition_dedup #54279)

Moves all but the first of consecutive elements to the end of the slice satisfying a given equality relation.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

The same_bucket function is passed references to two elements from the slice and must determine if the elements compare equal. The elements are passed in opposite order from their order in the slice, so if same_bucket(a, b) returns true, a is moved at the end of the slice.

If the slice is sorted, the first returned slice contains no duplicates.

§Examples

#![feature(slice_partition_dedup)] let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"]; let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b)); assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);

Run

source

🔬This is a nightly-only experimental API. (slice_partition_dedup #54279)

Moves all but the first of consecutive elements to the end of the slice that resolve to the same key.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

If the slice is sorted, the first returned slice contains no duplicates.

§Examples

#![feature(slice_partition_dedup)] let mut slice = [10, 20, 21, 30, 30, 20, 11, 13]; let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10); assert_eq!(dedup, [10, 20, 30, 20, 11]);
assert_eq!(duplicates, [21, 30, 13]);

Run

1.26.0 · source

Rotates the slice in-place such that the first mid elements of the slice move to the end while the last self.len() - mid elements move to the front. After calling rotate_left, the element previously at index mid will become the first element in the slice.

§Panics

This function will panic if mid is greater than the length of the slice. Note that mid == self.len() does not panic and is a no-op rotation.

§Complexity

Takes linear (in self.len()) time.

§Examples

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a.rotate_left(2);
assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);

Run

Rotating a subslice:

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a[1..5].rotate_left(1);
assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);

Run

1.26.0 · source

Rotates the slice in-place such that the first self.len() - k elements of the slice move to the end while the last k elements move to the front. After calling rotate_right, the element previously at index self.len() - k will become the first element in the slice.

§Panics

This function will panic if k is greater than the length of the slice. Note that k == self.len() does not panic and is a no-op rotation.

§Complexity

Takes linear (in self.len()) time.

§Examples

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a.rotate_right(2);
assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);

Run

Rotating a subslice:

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a[1..5].rotate_right(1);
assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);

Run

1.50.0 · source

Fills self with elements by cloning value.

§Examples

let mut buf = vec![0; 10];
buf.fill(1);
assert_eq!(buf, vec![1; 10]);

Run

1.51.0 · source

Fills self with elements returned by calling a closure repeatedly.

This method uses a closure to create new values. If you’d rather Clone a given value, use fill. If you want to use the Default trait to generate values, you can pass Default::default as the argument.

§Examples

let mut buf = vec![1; 10];
buf.fill_with(Default::default);
assert_eq!(buf, vec![0; 10]);

Run

1.7.0 · source

Copies the elements from src into self.

The length of src must be the same as self.

§Panics

This function will panic if the two slices have different lengths.

§Examples

Cloning two elements from a slice into another:

let src = [1, 2, 3, 4];
let mut dst = [0, 0]; dst.clone_from_slice(&src[2..]); assert_eq!(src, [1, 2, 3, 4]);
assert_eq!(dst, [3, 4]);

Run

Rust enforces that there can only be one mutable reference with no immutable references to a particular piece of data in a particular scope. Because of this, attempting to use clone_from_slice on a single slice will result in a compile failure:

ⓘ

let mut slice = [1, 2, 3, 4, 5]; slice[..2].clone_from_slice(&slice[3..]);

Run

To work around this, we can use split_at_mut to create two distinct sub-slices from a slice:

let mut slice = [1, 2, 3, 4, 5]; { let (left, right) = slice.split_at_mut(2); left.clone_from_slice(&right[1..]);
} assert_eq!(slice, [4, 5, 3, 4, 5]);

Run

1.9.0 · source

Copies all elements from src into self, using a memcpy.

The length of src must be the same as self.

If T does not implement Copy, use clone_from_slice.

§Panics

This function will panic if the two slices have different lengths.

§Examples

Copying two elements from a slice into another:

let src = [1, 2, 3, 4];
let mut dst = [0, 0]; dst.copy_from_slice(&src[2..]); assert_eq!(src, [1, 2, 3, 4]);
assert_eq!(dst, [3, 4]);

Run

Rust enforces that there can only be one mutable reference with no immutable references to a particular piece of data in a particular scope. Because of this, attempting to use copy_from_slice on a single slice will result in a compile failure:

ⓘ

let mut slice = [1, 2, 3, 4, 5]; slice[..2].copy_from_slice(&slice[3..]);

Run

To work around this, we can use split_at_mut to create two distinct sub-slices from a slice:

let mut slice = [1, 2, 3, 4, 5]; { let (left, right) = slice.split_at_mut(2); left.copy_from_slice(&right[1..]);
} assert_eq!(slice, [4, 5, 3, 4, 5]);

Run

1.37.0 · source

Copies elements from one part of the slice to another part of itself, using a memmove.

src is the range within self to copy from. dest is the starting index of the range within self to copy to, which will have the same length as src. The two ranges may overlap. The ends of the two ranges must be less than or equal to self.len().

§Panics

This function will panic if either range exceeds the end of the slice, or if the end of src is before the start.

§Examples

Copying four bytes within a slice:

let mut bytes = *b"Hello, World!"; bytes.copy_within(1..5, 8); assert_eq!(&bytes, b"Hello, Wello!");

Run

1.27.0 · source

Swaps all elements in self with those in other.

The length of other must be the same as self.

§Panics

This function will panic if the two slices have different lengths.

§Example

Swapping two elements across slices:

let mut slice1 = [0, 0];
let mut slice2 = [1, 2, 3, 4]; slice1.swap_with_slice(&mut slice2[2..]); assert_eq!(slice1, [3, 4]);
assert_eq!(slice2, [1, 2, 0, 0]);

Run

Rust enforces that there can only be one mutable reference to a particular piece of data in a particular scope. Because of this, attempting to use swap_with_slice on a single slice will result in a compile failure:

ⓘ

let mut slice = [1, 2, 3, 4, 5];
slice[..2].swap_with_slice(&mut slice[3..]);

Run

To work around this, we can use split_at_mut to create two distinct mutable sub-slices from a slice:

let mut slice = [1, 2, 3, 4, 5]; { let (left, right) = slice.split_at_mut(2); left.swap_with_slice(&mut right[1..]);
} assert_eq!(slice, [4, 5, 3, 1, 2]);

Run

1.30.0 · source

Transmute the slice to a slice of another type, ensuring alignment of the types is maintained.

This method splits the slice into three distinct slices: prefix, correctly aligned middle slice of a new type, and the suffix slice. The middle part will be as big as possible under the given alignment constraint and element size.

This method has no purpose when either input element T or output element U are zero-sized and will return the original slice without splitting anything.

§Safety

This method is essentially a transmute with respect to the elements in the returned middle slice, so all the usual caveats pertaining to transmute::<T, U> also apply here.

§Examples

Basic usage:

unsafe { let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7]; let (prefix, shorts, suffix) = bytes.align_to::<u16>();
    }

Run

1.30.0 · source

Transmute the mutable slice to a mutable slice of another type, ensuring alignment of the types is maintained.

This method has no purpose when either input element T or output element U are zero-sized and will return the original slice without splitting anything.

§Safety

This method is essentially a transmute with respect to the elements in the returned middle slice, so all the usual caveats pertaining to transmute::<T, U> also apply here.

§Examples

Basic usage:

unsafe { let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7]; let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
    }

Run

source

🔬This is a nightly-only experimental API. (portable_simd #86656)

Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.

This is a safe wrapper around slice::align_to, so inherits the same guarantees as that method.

§Panics

This will panic if the size of the SIMD type is different from LANES times that of the scalar.

At the time of writing, the trait restrictions on Simd<T, LANES> keeps that from ever happening, as only power-of-two numbers of lanes are supported. It’s possible that, in the future, those restrictions might be lifted in a way that would make it possible to see panics from this method for something like LANES == 3.

§Examples

#![feature(portable_simd)]
use core::simd::prelude::*; let short = &[1, 2, 3];
let (prefix, middle, suffix) = short.as_simd::<4>();
assert_eq!(middle, []); let it = prefix.iter().chain(suffix).copied();
assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]); fn basic_simd_sum(x: &[f32]) -> f32 { use std::ops::Add; let (prefix, middle, suffix) = x.as_simd(); let sums = f32x4::from_array([ prefix.iter().copied().sum(), 0.0, 0.0, suffix.iter().copied().sum(), ]); let sums = middle.iter().copied().fold(sums, f32x4::add); sums.reduce_sum()
} let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);

Run

source

🔬This is a nightly-only experimental API. (portable_simd #86656)

Split a mutable slice into a mutable prefix, a middle of aligned SIMD types, and a mutable suffix.

This is a safe wrapper around slice::align_to_mut, so inherits the same guarantees as that method.

This is the mutable version of slice::as_simd; see that for examples.

§Panics

This will panic if the size of the SIMD type is different from LANES times that of the scalar.

source

🔬This is a nightly-only experimental API. (is_sorted #53485)

Checks if the elements of this slice are sorted.

That is, for each element a and its following element b, a <= b must hold. If the slice yields exactly zero or one element, true is returned.

Note that if Self::Item is only PartialOrd, but not Ord, the above definition implies that this function returns false if any two consecutive items are not comparable.

§Examples

#![feature(is_sorted)]
let empty: [i32; 0] = []; assert!([1, 2, 2, 9].is_sorted());
assert!(![1, 3, 2, 4].is_sorted());
assert!([0].is_sorted());
assert!(empty.is_sorted());
assert!(![0.0, 1.0, f32::NAN].is_sorted());

Run

source

🔬This is a nightly-only experimental API. (is_sorted #53485)

Checks if the elements of this slice are sorted using the given comparator function.

Instead of using PartialOrd::partial_cmp, this function uses the given compare function to determine whether two elements are to be considered in sorted order.

§Examples

#![feature(is_sorted)] assert!([1, 2, 2, 9].is_sorted_by(|a, b| a <= b));
assert!(![1, 2, 2, 9].is_sorted_by(|a, b| a < b)); assert!([0].is_sorted_by(|a, b| true));
assert!([0].is_sorted_by(|a, b| false)); let empty: [i32; 0] = [];
assert!(empty.is_sorted_by(|a, b| false));
assert!(empty.is_sorted_by(|a, b| true));

Run

source

🔬This is a nightly-only experimental API. (is_sorted #53485)

Checks if the elements of this slice are sorted using the given key extraction function.

Instead of comparing the slice’s elements directly, this function compares the keys of the elements, as determined by f. Apart from that, it’s equivalent to is_sorted; see its documentation for more information.

§Examples

#![feature(is_sorted)] assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));

Run

1.52.0 · source

Returns the index of the partition point according to the given predicate (the index of the first element of the second partition).

The slice is assumed to be partitioned according to the given predicate. This means that all elements for which the predicate returns true are at the start of the slice and all elements for which the predicate returns false are at the end. For example, [7, 15, 3, 5, 4, 12, 6] is partitioned under the predicate x % 2 != 0 (all odd numbers are at the start, all even at the end).

If this slice is not partitioned, the returned result is unspecified and meaningless, as this method performs a kind of binary search.

§Examples

let v = [1, 2, 3, 3, 5, 6, 7];
let i = v.partition_point(|&x| x < 5); assert_eq!(i, 4);
assert!(v[..i].iter().all(|&x| x < 5));
assert!(v[i..].iter().all(|&x| !(x < 5)));

Run

If all elements of the slice match the predicate, including if the slice is empty, then the length of the slice will be returned:

let a = [2, 4, 8];
assert_eq!(a.partition_point(|x| x < &100), a.len());
let a: [i32; 0] = [];
assert_eq!(a.partition_point(|x| x < &100), 0);

Run

If you want to insert an item to a sorted vector, while maintaining sort order:

let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
let num = 42;
let idx = s.partition_point(|&x| x <= num);
s.insert(idx, num);
assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);

Run

source

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the subslice corresponding to the given range and returns a reference to it.

Returns None and does not modify the slice if the given range is out of bounds.

Note that this method only accepts one-sided ranges such as 2.. or ..6, but not 2..6.

§Examples

Taking the first three elements of a slice:

#![feature(slice_take)] let mut slice: &[_] = &['a', 'b', 'c', 'd'];
let mut first_three = slice.take(..3).unwrap(); assert_eq!(slice, &['d']);
assert_eq!(first_three, &['a', 'b', 'c']);

Run

Taking the last two elements of a slice:

#![feature(slice_take)] let mut slice: &[_] = &['a', 'b', 'c', 'd'];
let mut tail = slice.take(2..).unwrap(); assert_eq!(slice, &['a', 'b']);
assert_eq!(tail, &['c', 'd']);

Run

Getting None when range is out of bounds:

#![feature(slice_take)] let mut slice: &[_] = &['a', 'b', 'c', 'd']; assert_eq!(None, slice.take(5..));
assert_eq!(None, slice.take(..5));
assert_eq!(None, slice.take(..=4));
let expected: &[char] = &['a', 'b', 'c', 'd'];
assert_eq!(Some(expected), slice.take(..4));

Run

source

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the subslice corresponding to the given range and returns a mutable reference to it.

Returns None and does not modify the slice if the given range is out of bounds.

Note that this method only accepts one-sided ranges such as 2.. or ..6, but not 2..6.

§Examples

Taking the first three elements of a slice:

#![feature(slice_take)] let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
let mut first_three = slice.take_mut(..3).unwrap(); assert_eq!(slice, &mut ['d']);
assert_eq!(first_three, &mut ['a', 'b', 'c']);

Run

Taking the last two elements of a slice:

#![feature(slice_take)] let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
let mut tail = slice.take_mut(2..).unwrap(); assert_eq!(slice, &mut ['a', 'b']);
assert_eq!(tail, &mut ['c', 'd']);

Run

Getting None when range is out of bounds:

#![feature(slice_take)] let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd']; assert_eq!(None, slice.take_mut(5..));
assert_eq!(None, slice.take_mut(..5));
assert_eq!(None, slice.take_mut(..=4));
let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
assert_eq!(Some(expected), slice.take_mut(..4));

Run

source

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the first element of the slice and returns a reference to it.

Returns None if the slice is empty.

§Examples

#![feature(slice_take)] let mut slice: &[_] = &['a', 'b', 'c'];
let first = slice.take_first().unwrap(); assert_eq!(slice, &['b', 'c']);
assert_eq!(first, &'a');

Run

source

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the first element of the slice and returns a mutable reference to it.

Returns None if the slice is empty.

§Examples

#![feature(slice_take)] let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
let first = slice.take_first_mut().unwrap();
*first = 'd'; assert_eq!(slice, &['b', 'c']);
assert_eq!(first, &'d');

Run

source

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the last element of the slice and returns a reference to it.

Returns None if the slice is empty.

§Examples

#![feature(slice_take)] let mut slice: &[_] = &['a', 'b', 'c'];
let last = slice.take_last().unwrap(); assert_eq!(slice, &['a', 'b']);
assert_eq!(last, &'c');

Run

source

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the last element of the slice and returns a mutable reference to it.

Returns None if the slice is empty.

§Examples

#![feature(slice_take)] let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
let last = slice.take_last_mut().unwrap();
*last = 'd'; assert_eq!(slice, &['a', 'b']);
assert_eq!(last, &'d');

Run

source

🔬This is a nightly-only experimental API. (get_many_mut #104642)

Returns mutable references to many indices at once, without doing any checks.

For a safe alternative see get_many_mut.

§Safety

Calling this method with overlapping or out-of-bounds indices is undefined behavior even if the resulting references are not used.

§Examples

#![feature(get_many_mut)] let x = &mut [1, 2, 4]; unsafe { let [a, b] = x.get_many_unchecked_mut([0, 2]); *a *= 10; *b *= 100;
}
assert_eq!(x, &[10, 2, 400]);

Run

source

🔬This is a nightly-only experimental API. (get_many_mut #104642)

Returns mutable references to many indices at once.

Returns an error if any index is out-of-bounds, or if the same index was passed more than once.

§Examples

#![feature(get_many_mut)] let v = &mut [1, 2, 3];
if let Ok([a, b]) = v.get_many_mut([0, 2]) { *a = 413; *b = 612;
}
assert_eq!(v, &[413, 2, 612]);

Run

1.5.0 · source §

source §

Converts this type into a mutable reference of the (usually inferred) input type.

1.5.0 · source §

source §

Converts this type into a mutable reference of the (usually inferred) input type.

1.0.0 · source §

source §

Converts this type into a shared reference of the (usually inferred) input type.

1.0.0 · source §

source §

Converts this type into a shared reference of the (usually inferred) input type.

1.0.0 · source §

source §

Immutably borrows from an owned value. Read more

1.0.0 · source §

source §

Mutably borrows from an owned value. Read more

1.0.0 · source §

source §

Overwrites the contents of self with a clone of the contents of source.

This method is preferred over simply assigning source.clone() to self, as it avoids reallocation if possible. Additionally, if the element type T overrides clone_from(), this will reuse the resources of self’s elements as well.

§Examples

let x = vec![5, 6, 7];
let mut y = vec![8, 9, 10];
let yp: *const i32 = y.as_ptr(); y.clone_from(&x); assert_eq!(x, y); assert_eq!(yp, y.as_ptr());

Run

source §

Returns a copy of the value. Read more

1.0.0 · source §

source §

Formats the value using the given formatter. Read more

1.0.0 · source §

source §

Creates an empty Vec<T>.

The vector will not allocate until elements are pushed onto it.

1.0.0 · source §

The resulting type after dereferencing.

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1.0.0 · source §

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Mutably dereferences the value.

1.0.0 · source §

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Executes the destructor for this type. Read more

1.2.0 · source §

Extend implementation that copies elements out of references before pushing them onto the Vec.

This implementation is specialized for slice iterators, where it uses copy_from_slice to append the entire slice at once.

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Extends a collection with the contents of an iterator. Read more

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🔬This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

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🔬This is a nightly-only experimental API. (extend_one #72631)

Reserves capacity in a collection for the given number of additional elements. Read more

1.0.0 · source §

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Extends a collection with the contents of an iterator. Read more

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🔬This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

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🔬This is a nightly-only experimental API. (extend_one #72631)

Reserves capacity in a collection for the given number of additional elements. Read more

1.0.0 · source §

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Allocate a Vec<T> and fill it by cloning s’s items.

§Examples

assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);

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1.74.0 · source §

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Allocate a Vec<T> and fill it by cloning s’s items.

§Examples

assert_eq!(Vec::from(&[1, 2, 3]), vec![1, 2, 3]);

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1.28.0 · source §

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Creates a Borrowed variant of Cow from a reference to Vec.

This conversion does not allocate or clone the data.

1.19.0 · source §

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Allocate a Vec<T> and fill it by cloning s’s items.

§Examples

assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);

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1.74.0 · source §

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Allocate a Vec<T> and fill it by cloning s’s items.

§Examples

assert_eq!(Vec::from(&mut [1, 2, 3]), vec![1, 2, 3]);

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1.0.0 · source §

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Allocate a Vec<u8> and fill it with a UTF-8 string.

§Examples

assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);

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1.44.0 · source §

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Allocate a Vec<T> and move s’s items into it.

§Examples

assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);

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1.5.0 · source §

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Converts a BinaryHeap<T> into a Vec<T>.

This conversion requires no data movement or allocation, and has constant time complexity.

1.18.0 · source §

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Convert a boxed slice into a vector by transferring ownership of the existing heap allocation.

§Examples

let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
assert_eq!(Vec::from(b), vec![1, 2, 3]);

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1.7.0 · source §

1.14.0 · source §

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Convert a clone-on-write slice into a vector.

If s already owns a Vec<T>, it will be returned directly. If s is borrowing a slice, a new Vec<T> will be allocated and filled by cloning s’s items into it.

§Examples

let o: Cow<'_, [i32]> = Cow::Owned(vec![1, 2, 3]);
let b: Cow<'_, [i32]> = Cow::Borrowed(&[1, 2, 3]);
assert_eq!(Vec::from(o), Vec::from(b));

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1.14.0 · source §

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Converts the given String to a vector Vec that holds values of type u8.

§Examples

let s1 = String::from("hello world");
let v1 = Vec::from(s1); for b in v1 { println!("{b}");
}

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1.43.0 · source §

1.8.0 · source §

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Creates an Owned variant of Cow from an owned instance of Vec.

This conversion does not allocate or clone the data.

1.21.0 · source §

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Allocate a reference-counted slice and move v’s items into it.

§Example

let unique: Vec<i32> = vec![1, 2, 3];
let shared: Arc<[i32]> = Arc::from(unique);
assert_eq!(&[1, 2, 3], &shared[..]);

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1.5.0 · source §

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Converts a Vec<T> into a BinaryHeap<T>.

This conversion happens in-place, and has O(n) time complexity.

1.20.0 · source §

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Convert a vector into a boxed slice.

Before doing the conversion, this method discards excess capacity like Vec::shrink_to_fit.

§Examples

assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());

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Any excess capacity is removed:

let mut vec = Vec::with_capacity(10);
vec.extend([1, 2, 3]); assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());

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1.21.0 · source §

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Allocate a reference-counted slice and move v’s items into it.

§Example

let unique: Vec<i32> = vec![1, 2, 3];
let shared: Rc<[i32]> = Rc::from(unique);
assert_eq!(&[1, 2, 3], &shared[..]);

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1.10.0 · source §

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Turn a Vec<T> into a VecDeque<T>.

This conversion is guaranteed to run in O(1) time and to not re-allocate the Vec’s buffer or allocate any additional memory.

1.10.0 · source §

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Turn a VecDeque<T> into a Vec<T>.

This never needs to re-allocate, but does need to do O(n) data movement if the circular buffer doesn’t happen to be at the beginning of the allocation.

§Examples

use std::collections::VecDeque; let deque: VecDeque<_> = (1..5).collect();
let ptr = deque.as_slices().0.as_ptr();
let vec = Vec::from(deque);
assert_eq!(vec, [1, 2, 3, 4]);
assert_eq!(vec.as_ptr(), ptr); let mut deque: VecDeque<_> = (1..5).collect();
deque.push_front(9);
deque.push_front(8);
let ptr = deque.as_slices().1.as_ptr();
let vec = Vec::from(deque);
assert_eq!(vec, [8, 9, 1, 2, 3, 4]);
assert_eq!(vec.as_ptr(), ptr);

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1.0.0 · source §

Collects an iterator into a Vec, commonly called via Iterator::collect()

§Allocation behavior

In general Vec does not guarantee any particular growth or allocation strategy. That also applies to this trait impl.

Note: This section covers implementation details and is therefore exempt from stability guarantees.

Vec may use any or none of the following strategies, depending on the supplied iterator:

preallocate based on Iterator::size_hint()
- and panic if the number of items is outside the provided lower/upper bounds
use an amortized growth strategy similar to pushing one item at a time
perform the iteration in-place on the original allocation backing the iterator

The last case warrants some attention. It is an optimization that in many cases reduces peak memory consumption and improves cache locality. But when big, short-lived allocations are created, only a small fraction of their items get collected, no further use is made of the spare capacity and the resulting Vec is moved into a longer-lived structure, then this can lead to the large allocations having their lifetimes unnecessarily extended which can result in increased memory footprint.

In cases where this is an issue, the excess capacity can be discarded with Vec::shrink_to(), Vec::shrink_to_fit() or by collecting into Box<[T]> instead, which additionally reduces the size of the long-lived struct.

static LONG_LIVED: Mutex<Vec<Vec<u16>>> = Mutex::new(Vec::new()); for i in 0..10 { let big_temporary: Vec<u16> = (0..1024).collect(); let mut result: Vec<_> = big_temporary.into_iter().filter(|i| i % 100 == 0).collect();
    result.shrink_to_fit();
    LONG_LIVED.lock().unwrap().push(result);
}

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Creates a value from an iterator. Read more

1.0.0 · source §

The hash of a vector is the same as that of the corresponding slice, as required by the core::borrow::Borrow implementation.

use std::hash::BuildHasher; let b = std::hash::RandomState::new();
let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
let s: &[u8] = &[0xa8, 0x3c, 0x09];
assert_eq!(b.hash_one(v), b.hash_one(s));

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1.0.0 · source §

The returned type after indexing.

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Performs the indexing (container[index]) operation. Read more

1.0.0 · source §

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

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Creates an iterator from a value. Read more

1.0.0 · source §

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

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Creates an iterator from a value. Read more

1.0.0 · source §

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Creates a consuming iterator, that is, one that moves each value out of the vector (from start to end). The vector cannot be used after calling this.

§Examples

let v = vec!["a".to_string(), "b".to_string()];
let mut v_iter = v.into_iter(); let first_element: Option<String> = v_iter.next(); assert_eq!(first_element, Some("a".to_string()));
assert_eq!(v_iter.next(), Some("b".to_string()));
assert_eq!(v_iter.next(), None);

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The type of the elements being iterated over.

Which kind of iterator are we turning this into?

1.0.0 · source §

Implements ordering of vectors, lexicographically.

1.0.0 · source §

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