//! A contiguous growable array type with heap-allocated contents, written
//! `Vec<T>`.
//!
//! Vectors have *O*(1) indexing, amortized *O*(1) push (to the end) and
//! *O*(1) pop (from the end).
//!
//! Vectors ensure they never allocate more than `isize::MAX` bytes.
//!
//! # Examples
//!
//! You can explicitly create a [`Vec`] with [`Vec::new`]:
//!
//! ```
//! let v: Vec<i32> = Vec::new();
//! ```
//!
//! ...or by using the [`vec!`] macro:
//!
//! ```
//! let v: Vec<i32> = vec![];
//!
//! let v = vec![1, 2, 3, 4, 5];
//!
//! let v = vec![0; 10]; // ten zeroes
//! ```
//!
//! You can [`push`] values onto the end of a vector (which will grow the vector
//! as needed):
//!
//! ```
//! let mut v = vec![1, 2];
//!
//! v.push(3);
//! ```
//!
//! Popping values works in much the same way:
//!
//! ```
//! let mut v = vec![1, 2];
//!
//! let two = v.pop();
//! ```
//!
//! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
//!
//! ```
//! let mut v = vec![1, 2, 3];
//! let three = v[2];
//! v[1] = v[1] + 5;
//! ```
//!
//! [`push`]: Vec::push
#[cfg(not(no_global_oom_handling))]
use core::cmp;
use core::cmp::Ordering;
use core::convert::TryFrom;
use core::fmt;
use core::hash::{Hash, Hasher};
#[cfg(not(no_global_oom_handling))]
use core::iter;
#[cfg(not(no_global_oom_handling))]
use core::iter::FromIterator;
use core::marker::PhantomData;
use core::mem::{self, size_of, ManuallyDrop, MaybeUninit};
use core::ops::{self, Bound, Index, IndexMut, Range, RangeBounds};
use core::ptr::{self, NonNull};
use core::slice::{self, SliceIndex};
#[cfg(feature = "std")]
use std::io;
use super::{
alloc::{Allocator, Global},
assume,
boxed::Box,
raw_vec::{RawVec, TryReserveError},
};
#[cfg(not(no_global_oom_handling))]
pub use self::splice::Splice;
#[cfg(not(no_global_oom_handling))]
mod splice;
pub use self::drain::Drain;
mod drain;
pub use self::into_iter::IntoIter;
mod into_iter;
mod partial_eq;
#[cfg(not(no_global_oom_handling))]
mod set_len_on_drop;
#[cfg(not(no_global_oom_handling))]
use self::set_len_on_drop::SetLenOnDrop;
/// 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].iter().copied());
///
/// for x in &vec {
/// println!("{x}");
/// }
/// assert_eq!(vec, [7, 1, 2, 3]);
/// ```
///
/// 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);
/// ```
///
/// 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]);
///
/// // The following is equivalent, but potentially slower:
/// let mut vec = Vec::with_capacity(5);
/// vec.resize(5, 0);
/// assert_eq!(vec, [0, 0, 0, 0, 0]);
/// ```
///
/// For more information, see
/// [Capacity and Reallocation](#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() {
/// // Prints 3, 2, 1
/// println!("{top}");
/// }
/// ```
///
/// # Indexing
///
/// The `Vec` type allows to access 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]); // it will display '2'
/// ```
///
/// However be careful: if you try to access an index which isn't in the `Vec`,
/// your software will panic! You cannot do this:
///
/// ```should_panic
/// let v = vec![0, 2, 4, 6];
/// println!("{}", v[6]); // it will panic!
/// ```
///
/// 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][prim@slice], use [`&`]. Example:
///
/// ```
/// fn read_slice(slice: &[usize]) {
/// // ...
/// }
///
/// let v = vec![0, 1];
/// read_slice(&v);
///
/// // ... and that's all!
/// // you can also do it like this:
/// let u: &[usize] = &v;
/// // or like this:
/// let u: &[_] = &v;
/// ```
///
/// 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!`],
/// [`Vec::with_capacity(0)`][`Vec::with_capacity`], 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 <code>[mem::size_of::\<T>]\() * [capacity]\() > 0</code>. 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 <code>[capacity] - [len]</code>
/// 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.
///
/// ```text
/// 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
/// <code>[len] == [capacity]</code>. 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)`][`Vec::with_capacity`], will all produce a `Vec`
/// with exactly the requested capacity. If <code>[len] == [capacity]</code>,
/// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
/// and from a [`Box<[T]>`][owned slice] 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.
///
/// [`get`]: ../../std/vec/struct.Vec.html#method.get
/// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut
/// [`String`]: alloc_crate::string::String
/// [`&str`]: type@str
/// [`shrink_to_fit`]: Vec::shrink_to_fit
/// [`shrink_to`]: Vec::shrink_to
/// [capacity]: Vec::capacity
/// [`capacity`]: Vec::capacity
/// [mem::size_of::\<T>]: core::mem::size_of
/// [len]: Vec::len
/// [`len`]: Vec::len
/// [`push`]: Vec::push
/// [`insert`]: Vec::insert
/// [`reserve`]: Vec::reserve
/// [`MaybeUninit`]: core::mem::MaybeUninit
/// [owned slice]: Box
pub struct Vec<T, A: Allocator = Global> {
buf: RawVec<T, A>,
len: usize,
}
////////////////////////////////////////////////////////////////////////////////
// Inherent methods
////////////////////////////////////////////////////////////////////////////////
impl<T> Vec<T> {
/// Constructs a new, empty `Vec<T>`.
///
/// The vector will not allocate until elements are pushed onto it.
///
/// # Examples
///
/// ```
/// # #![allow(unused_mut)]
/// let mut vec: Vec<i32> = Vec::new();
/// ```
#[inline(always)]
#[must_use]
pub const fn new() -> Self {
Vec {
buf: RawVec::new(),
len: 0,
}
}
/// 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`.
///
/// [Capacity and reallocation]: #capacity-and-reallocation
/// [`capacity`]: Vec::capacity
///
/// # Panics
///
/// Panics if the new capacity exceeds `isize::MAX` bytes.
///
/// # Examples
///
/// ```
/// let mut vec = Vec::with_capacity(10);
///
/// // The vector contains no items, even though it has capacity for more
/// assert_eq!(vec.len(), 0);
/// assert!(vec.capacity() >= 10);
///
/// // These are all done without reallocating...
/// for i in 0..10 {
/// vec.push(i);
/// }
/// assert_eq!(vec.len(), 10);
/// assert!(vec.capacity() >= 10);
///
/// // ...but this may make the vector reallocate
/// vec.push(11);
/// assert_eq!(vec.len(), 11);
/// assert!(vec.capacity() >= 11);
///
/// // A vector of a zero-sized type will always over-allocate, since no
/// // allocation is necessary
/// let vec_units = Vec::<()>::with_capacity(10);
/// assert_eq!(vec_units.capacity(), usize::MAX);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline(always)]
#[must_use]
pub fn with_capacity(capacity: usize) -> Self {
Self::with_capacity_in(capacity, Global)
}
/// Creates a `Vec<T>` directly from a pointer, a capacity, and a length.
///
/// # Safety
///
/// This is highly unsafe, due to the number of invariants that aren't
/// checked:
///
/// * `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`](
https://doc.rust-lang.org/nightly/std/primitive.pointer.html#method.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.
///
/// [`String`]: alloc_crate::string::String
/// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
///
/// # Examples
///
/// ```
/// use std::ptr;
/// use std::mem;
///
/// let v = vec![1, 2, 3];
///
// FIXME Update this when vec_into_raw_parts is stabilized
/// // Prevent running `v`'s destructor so we are in complete control
/// // of the allocation.
/// let mut v = mem::ManuallyDrop::new(v);
///
/// // Pull out the various important pieces of information about `v`
/// let p = v.as_mut_ptr();
/// let len = v.len();
/// let cap = v.capacity();
///
/// unsafe {
/// // Overwrite memory with 4, 5, 6
/// for i in 0..len {
/// ptr::write(p.add(i), 4 + i);
/// }
///
/// // Put everything back together into a Vec
/// let rebuilt = Vec::from_raw_parts(p, len, cap);
/// assert_eq!(rebuilt, [4, 5, 6]);
/// }
/// ```
///
/// Using memory that was allocated elsewhere:
///
/// ```rust
/// #![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);
/// }
/// ```
#[inline(always)]
pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
}
}
impl<T, A: Allocator> Vec<T, A> {
/// Constructs a new, empty `Vec<T, A>`.
///
/// The vector will not allocate until elements are pushed onto it.
///
/// # Examples
///
/// ```
/// use std::alloc::System;
///
/// # #[allow(unused_mut)]
/// let mut vec: Vec<i32, _> = Vec::new_in(System);
/// ```
#[inline(always)]
pub const fn new_in(alloc: A) -> Self {
Vec {
buf: RawVec::new_in(alloc),
len: 0,
}
}
/// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
/// with the provided allocator.
///
/// 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, A>` where `T` is a zero-sized type, there will be no allocation
/// and the capacity will always be `usize::MAX`.
///
/// [Capacity and reallocation]: #capacity-and-reallocation
/// [`capacity`]: Vec::capacity
///
/// # Panics
///
/// Panics if the new capacity exceeds `isize::MAX` bytes.
///
/// # Examples
///
/// ```
/// use std::alloc::System;
///
/// let mut vec = Vec::with_capacity_in(10, System);
///
/// // The vector contains no items, even though it has capacity for more
/// assert_eq!(vec.len(), 0);
/// assert_eq!(vec.capacity(), 10);
///
/// // These are all done without reallocating...
/// for i in 0..10 {
/// vec.push(i);
/// }
/// assert_eq!(vec.len(), 10);
/// assert_eq!(vec.capacity(), 10);
///
/// // ...but this may make the vector reallocate
/// vec.push(11);
/// assert_eq!(vec.len(), 11);
/// assert!(vec.capacity() >= 11);
///
/// // A vector of a zero-sized type will always over-allocate, since no
/// // allocation is necessary
/// let vec_units = Vec::<(), System>::with_capacity_in(10, System);
/// assert_eq!(vec_units.capacity(), usize::MAX);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline(always)]
pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
Vec {
buf: RawVec::with_capacity_in(capacity, alloc),
len: 0,
}
}
/// Creates a `Vec<T, A>` directly from a pointer, a capacity, a length,
/// and an allocator.
///
/// # Safety
///
/// This is highly unsafe, due to the number of invariants that aren't
/// checked:
///
/// * `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`](
https://doc.rust-lang.org/nightly/std/primitive.pointer.html#method.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.
///
/// 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.
///
/// [`String`]: alloc_crate::string::String
/// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
/// [*fit*]: crate::alloc::Allocator#memory-fitting
///
/// # Examples
///
/// ```
/// use std::alloc::System;
///
/// use std::ptr;
/// use std::mem;
///
///
/// # use allocator_api2::vec::Vec;
/// let mut v = Vec::with_capacity_in(3, System);
/// v.push(1);
/// v.push(2);
/// v.push(3);
///
// FIXME Update this when vec_into_raw_parts is stabilized
/// // Prevent running `v`'s destructor so we are in complete control
/// // of the allocation.
/// let mut v = mem::ManuallyDrop::new(v);
///
/// // Pull out the various important pieces of information about `v`
/// let p = v.as_mut_ptr();
/// let len = v.len();
/// let cap = v.capacity();
/// let alloc = v.allocator();
///
/// unsafe {
/// // Overwrite memory with 4, 5, 6
/// for i in 0..len {
/// ptr::write(p.add(i), 4 + i);
/// }
///
/// // Put everything back together into a Vec
/// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
/// assert_eq!(rebuilt, [4, 5, 6]);
/// }
/// ```
///
/// Using memory that was allocated elsewhere:
///
/// ```rust
/// 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);
/// }
/// ```
#[inline(always)]
pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self
{
unsafe {
Vec {
buf: RawVec::from_raw_parts_in(ptr, capacity, alloc),
len: length,
}
}
}
/// Decomposes a `Vec<T>` into its raw components.
///
/// 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.
///
/// [`from_raw_parts`]: Vec::from_raw_parts
///
/// # 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 {
/// // We can now make changes to the components, such as
/// // transmuting the raw pointer to a compatible type.
/// let ptr = ptr as *mut u32;
///
/// Vec::from_raw_parts(ptr, len, cap)
/// };
/// assert_eq!(rebuilt, [4294967295, 0, 1]);
/// ```
pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
let mut me = ManuallyDrop::new(self);
(me.as_mut_ptr(), me.len(), me.capacity())
}
/// Decomposes a `Vec<T>` into its raw components.
///
/// 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.
///
/// [`from_raw_parts_in`]: Vec::from_raw_parts_in
///
/// # 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 {
/// // We can now make changes to the components, such as
/// // transmuting the raw pointer to a compatible type.
/// let ptr = ptr as *mut u32;
///
/// Vec::from_raw_parts_in(ptr, len, cap, alloc)
/// };
/// assert_eq!(rebuilt, [4294967295, 0, 1]);
/// ```
// #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
let mut me = ManuallyDrop::new(self);
let len = me.len();
let capacity = me.capacity();
let ptr = me.as_mut_ptr();
let alloc = unsafe { ptr::read(me.allocator()) };
(ptr, len, capacity, alloc)
}
/// 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_eq!(vec.capacity(), 10);
/// ```
#[inline(always)]
pub fn capacity(&self) -> usize {
self.buf.capacity()
}
/// 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);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline(always)]
pub fn reserve(&mut self, additional: usize) {
self.buf.reserve(self.len, additional);
}
/// 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.
///
/// [`reserve`]: Vec::reserve
///
/// # Panics
///
/// Panics if the new capacity exceeds `isize::MAX` bytes.
///
/// # Examples
///
/// ```
/// let mut vec = vec![1];
/// vec.reserve_exact(10);
/// assert!(vec.capacity() >= 11);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline(always)]
pub fn reserve_exact(&mut self, additional: usize) {
self.buf.reserve_exact(self.len, additional);
}
/// 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();
///
/// // Pre-reserve the memory, exiting if we can't
/// output.try_reserve(data.len())?;
///
/// // Now we know this can't OOM in the middle of our complex work
/// output.extend(data.iter().map(|&val| {
/// val * 2 + 5 // very complicated
/// }));
///
/// Ok(output)
/// }
/// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
/// ```
#[inline(always)]
pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
self.buf.try_reserve(self.len, additional)
}
/// 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.
///
/// [`try_reserve`]: Vec::try_reserve
///
/// # 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();
///
/// // Pre-reserve the memory, exiting if we can't
/// output.try_reserve_exact(data.len())?;
///
/// // Now we know this can't OOM in the middle of our complex work
/// output.extend(data.iter().map(|&val| {
/// val * 2 + 5 // very complicated
/// }));
///
/// Ok(output)
/// }
/// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
/// ```
#[inline(always)]
pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
self.buf.try_reserve_exact(self.len, additional)
}
/// Shrinks the capacity of the vector as much as possible.
///
/// It will drop down as close as possible to the length but the allocator
/// may still inform the vector that there is space for a few more elements.
///
/// # Examples
///
/// ```
/// let mut vec = Vec::with_capacity(10);
/// vec.extend([1, 2, 3]);
/// assert_eq!(vec.capacity(), 10);
/// vec.shrink_to_fit();
/// assert!(vec.capacity() >= 3);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline(always)]
pub fn shrink_to_fit(&mut self) {
// The capacity is never less than the length, and there's nothing to do when
// they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
// by only calling it with a greater capacity.
if self.capacity() > self.len {
self.buf.shrink_to_fit(self.len);
}
}
/// 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_eq!(vec.capacity(), 10);
/// vec.shrink_to(4);
/// assert!(vec.capacity() >= 4);
/// vec.shrink_to(0);
/// assert!(vec.capacity() >= 3);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline(always)]
pub fn shrink_to(&mut self, min_capacity: usize) {
if self.capacity() > min_capacity {
self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
}
}
/// Converts the vector into [`Box<[T]>`][owned slice].
///
/// If the vector has excess capacity, its items will be moved into a
/// newly-allocated buffer with exactly the right capacity.
///
/// [owned slice]: Box
///
/// # Examples
///
/// ```
/// let v = vec![1, 2, 3];
///
/// let slice = v.into_boxed_slice();
/// ```
///
/// Any excess capacity is removed:
///
/// ```
/// let mut vec = Vec::with_capacity(10);
/// vec.extend([1, 2, 3]);
///
/// assert_eq!(vec.capacity(), 10);
/// let slice = vec.into_boxed_slice();
/// assert_eq!(slice.into_vec().capacity(), 3);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline(always)]
pub(crate) fn into_boxed_slice(mut self) -> Box<[T], A> {
unsafe {
self.shrink_to_fit();
let me = ManuallyDrop::new(self);
let buf = ptr::read(&me.buf);
let len = me.len();
buf.into_box(len).assume_init()
}
}
/// Shortens the vector, keeping the first `len` elements and dropping
/// the rest.
///
/// If `len` is greater than 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]);
/// ```
///
/// 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]);
/// ```
///
/// Truncating when `len == 0` is equivalent to calling the [`clear`]
/// method.
///
/// ```
/// let mut vec = vec![1, 2, 3];
/// vec.truncate(0);
/// assert_eq!(vec, []);
/// ```
///
/// [`clear`]: Vec::clear
/// [`drain`]: Vec::drain
#[inline(always)]
pub fn truncate(&mut self, len: usize) {
// This is safe because:
//
// * the slice passed to `drop_in_place` is valid; the `len > self.len`
// case avoids creating an invalid slice, and
// * the `len` of the vector is shrunk before calling `drop_in_place`,
// such that no value will be dropped twice in case `drop_in_place`
// were to panic once (if it panics twice, the program aborts).
unsafe {
// Note: It's intentional that this is `>` and not `>=`.
// Changing it to `>=` has negative performance
// implications in some cases. See #78884 for more.
if len > self.len {
return;
}
let remaining_len = self.len - len;
let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
self.len = len;
ptr::drop_in_place(s);
}
}
/// 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();
/// ```
#[inline(always)]
pub fn as_slice(&self) -> &[T] {
self
}
/// 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();
/// ```
#[inline(always)]
pub fn as_mut_slice(&mut self) -> &mut [T] {
self
}
/// 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`].
///
/// # 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);
/// }
/// }
/// ```
///
/// [`as_mut_ptr`]: Vec::as_mut_ptr
#[inline(always)]
pub fn as_ptr(&self) -> *const T {
// We shadow the slice method of the same name to avoid going through
// `deref`, which creates an intermediate reference.
let ptr = self.buf.ptr();
unsafe {
assume(!ptr.is_null());
}
ptr
}
/// 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.
///
/// 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.
///
/// # Examples
///
/// ```
/// // Allocate vector big enough for 4 elements.
/// let size = 4;
/// let mut x: Vec<i32> = Vec::with_capacity(size);
/// let x_ptr = x.as_mut_ptr();
///
/// // Initialize elements via raw pointer writes, then set length.
/// unsafe {
/// for i in 0..size {
/// *x_ptr.add(i) = i as i32;
/// }
/// x.set_len(size);
/// }
/// assert_eq!(&*x, &[0, 1, 2, 3]);
/// ```
#[inline(always)]
pub fn as_mut_ptr(&mut self) -> *mut T {
// We shadow the slice method of the same name to avoid going through
// `deref_mut`, which creates an intermediate reference.
let ptr = self.buf.ptr();
unsafe {
assume(!ptr.is_null());
}
ptr
}
/// Returns a reference to the underlying allocator.
#[inline(always)]
pub fn allocator(&self) -> &A {
self.buf.allocator()
}
/// 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`].
///
/// [`truncate`]: Vec::truncate
/// [`resize`]: Vec::resize
/// [`extend`]: Extend::extend
/// [`clear`]: Vec::clear
///
/// # Safety
///
/// - `new_len` must be less than or equal to [`capacity()`].
/// - The elements at `old_len..new_len` must be initialized.
///
/// [`capacity()`]: Vec::capacity
///
/// # Examples
///
/// This method can be useful for situations in which the vector
/// is serving as a buffer for other code, particularly over FFI:
///
/// ```no_run
/// # #![allow(dead_code)]
/// # // This is just a minimal skeleton for the doc example;
/// # // don't use this as a starting point for a real library.
/// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
/// # const Z_OK: i32 = 0;
/// # extern "C" {
/// # fn deflateGetDictionary(
/// # strm: *mut std::ffi::c_void,
/// # dictionary: *mut u8,
/// # dictLength: *mut usize,
/// # ) -> i32;
/// # }
/// # impl StreamWrapper {
/// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
/// // Per the FFI method's docs, "32768 bytes is always enough".
/// let mut dict = Vec::with_capacity(32_768);
/// let mut dict_length = 0;
/// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
/// // 1. `dict_length` elements were initialized.
/// // 2. `dict_length` <= the capacity (32_768)
/// // which makes `set_len` safe to call.
/// unsafe {
/// // Make the FFI call...
/// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
/// if r == Z_OK {
/// // ...and update the length to what was initialized.
/// dict.set_len(dict_length);
/// Some(dict)
/// } else {
/// None
/// }
/// }
/// }
/// # }
/// ```
///
/// 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]];
/// // SAFETY:
/// // 1. `old_len..0` is empty so no elements need to be initialized.
/// // 2. `0 <= capacity` always holds whatever `capacity` is.
/// unsafe {
/// vec.set_len(0);
/// }
/// ```
///
/// Normally, here, one would use [`clear`] instead to correctly drop
/// the contents and thus not leak memory.
#[inline(always)]
pub unsafe fn set_len(&mut self, new_len: usize) {
debug_assert!(new_len <= self.capacity());
self.len = new_len;
}
/// 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, but is *O*(1).
/// If you need to preserve the element order, use [`remove`] instead.
///
/// [`remove`]: Vec::remove
///
/// # 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"]);
/// ```
#[inline(always)]
pub fn swap_remove(&mut self, index: usize) -> T {
#[cold]
#[inline(never)]
fn assert_failed(index: usize, len: usize) -> ! {
panic!(
"swap_remove index (is {}) should be < len (is {})",
index, len
);
}
let len = self.len();
if index >= len {
assert_failed(index, len);
}
unsafe {
// We replace self[index] with the last element. Note that if the
// bounds check above succeeds there must be a last element (which
// can be self[index] itself).
let value = ptr::read(self.as_ptr().add(index));
let base_ptr = self.as_mut_ptr();
ptr::copy(base_ptr.add(len - 1), base_ptr.add(index), 1);
self.set_len(len - 1);
value
}
}
/// 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]);
/// ```
#[cfg(not(no_global_oom_handling))]
pub fn insert(&mut self, index: usize, element: T) {
#[cold]
#[inline(never)]
fn assert_failed(index: usize, len: usize) -> ! {
panic!(
"insertion index (is {}) should be <= len (is {})",
index, len
);
}
let len = self.len();
// space for the new element
if len == self.buf.capacity() {
self.reserve(1);
}
unsafe {
// infallible
// The spot to put the new value
{
let p = self.as_mut_ptr().add(index);
match cmp::Ord::cmp(&index, &len) {
Ordering::Less => {
// Shift everything over to make space. (Duplicating the
// `index`th element into two consecutive places.)
ptr::copy(p, p.add(1), len - index);
}
Ordering::Equal => {
// No elements need shifting.
}
Ordering::Greater => {
assert_failed(index, len);
}
}
// Write it in, overwriting the first copy of the `index`th
// element.
ptr::write(p, element);
}
self.set_len(len + 1);
}
}
/// 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.
///
/// [`swap_remove`]: Vec::swap_remove
/// [`VecDeque::pop_front`]: alloc_crate::collections::VecDeque::pop_front
///
/// # 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]);
/// ```
#[track_caller]
#[inline(always)]
pub fn remove(&mut self, index: usize) -> T {
#[cold]
#[inline(never)]
#[track_caller]
fn assert_failed(index: usize, len: usize) -> ! {
panic!("removal index (is {}) should be < len (is {})", index, len);
}
let len = self.len();
if index >= len {
assert_failed(index, len);
}
unsafe {
// infallible
let ret;
{
// the place we are taking from.
let ptr = self.as_mut_ptr().add(index);
// copy it out, unsafely having a copy of the value on
// the stack and in the vector at the same time.
ret = ptr::read(ptr);
// Shift everything down to fill in that spot.
ptr::copy(ptr.add(1), ptr, len - index - 1);
}
self.set_len(len - 1);
ret
}
}
/// 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]);
/// ```
///
/// 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]);
/// ```
#[inline(always)]
pub fn retain<F>(&mut self, mut f: F)
where
F: FnMut(&T) -> bool,
{
self.retain_mut(|elem| f(elem));
}
/// 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]);
/// ```
#[inline]
pub fn retain_mut<F>(&mut self, mut f: F)
where
F: FnMut(&mut T) -> bool,
{
let original_len = self.len();
// Avoid double drop if the drop guard is not executed,
// since we may make some holes during the process.
unsafe { self.set_len(0) };
// Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
// |<- processed len ->| ^- next to check
// |<- deleted cnt ->|
// |<- original_len ->|
// Kept: Elements which predicate returns true on.
// Hole: Moved or dropped element slot.
// Unchecked: Unchecked valid elements.
//
// This drop guard will be invoked when predicate or `drop` of element panicked.
// It shifts unchecked elements to cover holes and `set_len` to the correct length.
// In cases when predicate and `drop` never panick, it will be optimized out.
struct BackshiftOnDrop<'a, T, A: Allocator> {
v: &'a mut Vec<T, A>,
processed_len: usize,
deleted_cnt: usize,
original_len: usize,
}
impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
fn drop(&mut self) {
if self.deleted_cnt > 0 {
// SAFETY: Trailing unchecked items must be valid since we never touch them.
unsafe {
ptr::copy(
self.v.as_ptr().add(self.processed_len),
self.v
.as_mut_ptr()
.add(self.processed_len - self.deleted_cnt),
self.original_len - self.processed_len,
);
}
}
// SAFETY: After filling holes, all items are in contiguous memory.
unsafe {
self.v.set_len(self.original_len - self.deleted_cnt);
}
}
}
let mut g = BackshiftOnDrop {
v: self,
processed_len: 0,
deleted_cnt: 0,
original_len,
};
fn process_loop<F, T, A: Allocator, const DELETED: bool>(
original_len: usize,
f: &mut F,
g: &mut BackshiftOnDrop<'_, T, A>,
) where
F: FnMut(&mut T) -> bool,
{
while g.processed_len != original_len {
// SAFETY: Unchecked element must be valid.
let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
if !f(cur) {
// Advance early to avoid double drop if `drop_in_place` panicked.
g.processed_len += 1;
g.deleted_cnt += 1;
// SAFETY: We never touch this element again after dropped.
unsafe { ptr::drop_in_place(cur) };
// We already advanced the counter.
if DELETED {
continue;
} else {
break;
}
}
if DELETED {
// SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
// We use copy for move, and never touch this element again.
unsafe {
let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
ptr::copy_nonoverlapping(cur, hole_slot, 1);
}
}
g.processed_len += 1;
}
}
// Stage 1: Nothing was deleted.
process_loop::<F, T, A, false>(original_len, &mut f, &mut g);
// Stage 2: Some elements were deleted.
process_loop::<F, T, A, true>(original_len, &mut f, &mut g);
// All item are processed. This can be optimized to `set_len` by LLVM.
drop(g);
}
/// 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]);
/// ```
#[inline(always)]
pub fn dedup_by_key<F, K>(&mut self, mut key: F)
where
F: FnMut(&mut T) -> K,
K: PartialEq,
{
self.dedup_by(|a, b| key(a) == key(b))
}
/// 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"]);
/// ```
#[inline]
pub fn dedup_by<F>(&mut self, mut same_bucket: F)
where
F: FnMut(&mut T, &mut T) -> bool,
{
let len = self.len();
if len <= 1 {
return;
}
/* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
struct FillGapOnDrop<'a, T, A: Allocator> {
/* Offset of the element we want to check if it is duplicate */
read: usize,
/* Offset of the place where we want to place the non-duplicate
* when we find it. */
write: usize,
/* The Vec that would need correction if `same_bucket` panicked */
vec: &'a mut Vec<T, A>,
}
impl<'a, T, A: Allocator> Drop for FillGapOnDrop<'a, T, A> {
fn drop(&mut self) {
/* This code gets executed when `same_bucket` panics */
/* SAFETY: invariant guarantees that `read - write`
* and `len - read` never overflow and that the copy is always
* in-bounds. */
unsafe {
let ptr = self.vec.as_mut_ptr();
let len = self.vec.len();
/* How many items were left when `same_bucket` panicked.
* Basically vec[read..].len() */
let items_left = len.wrapping_sub(self.read);
/* Pointer to first item in vec[write..write+items_left] slice */
let dropped_ptr = ptr.add(self.write);
/* Pointer to first item in vec[read..] slice */
let valid_ptr = ptr.add(self.read);
/* Copy `vec[read..]` to `vec[write..write+items_left]`.
* The slices can overlap, so `copy_nonoverlapping` cannot be used */
ptr::copy(valid_ptr, dropped_ptr, items_left);
/* How many items have been already dropped
* Basically vec[read..write].len() */
let dropped = self.read.wrapping_sub(self.write);
self.vec.set_len(len - dropped);
}
}
}
let mut gap = FillGapOnDrop {
read: 1,
write: 1,
vec: self,
};
let ptr = gap.vec.as_mut_ptr();
/* Drop items while going through Vec, it should be more efficient than
* doing slice partition_dedup + truncate */
/* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
* are always in-bounds and read_ptr never aliases prev_ptr */
unsafe {
while gap.read < len {
let read_ptr = ptr.add(gap.read);
let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
// Increase `gap.read` now since the drop may panic.
gap.read += 1;
/* We have found duplicate, drop it in-place */
ptr::drop_in_place(read_ptr);
} else {
let write_ptr = ptr.add(gap.write);
/* Because `read_ptr` can be equal to `write_ptr`, we either
* have to use `copy` or conditional `copy_nonoverlapping`.
* Looks like the first option is faster. */
ptr::copy(read_ptr, write_ptr, 1);
/* We have filled that place, so go further */
gap.write += 1;
gap.read += 1;
}
}
/* Technically we could let `gap` clean up with its Drop, but
* when `same_bucket` is guaranteed to not panic, this bloats a little
* the codegen, so we just do it manually */
gap.vec.set_len(gap.write);
mem::forget(gap);
}
}
/// 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]);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline(always)]
pub fn push(&mut self, value: T) {
// This will panic or abort if we would allocate > isize::MAX bytes
// or if the length increment would overflow for zero-sized types.
if self.len == self.buf.capacity() {
self.buf.reserve_for_push(self.len);
}
unsafe {
let end = self.as_mut_ptr().add(self.len);
ptr::write(end, value);
self.len += 1;
}
}
/// 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.
///
/// [`push`]: Vec::push
/// [`reserve`]: Vec::reserve
/// [`try_reserve`]: Vec::try_reserve
///
/// # 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)?;
/// // this cannot fail, the previous line either returned or added at least 1 free slot
/// let _ = vec.push_within_capacity(value);
/// }
/// }
/// Ok(vec)
/// }
/// assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));
/// ```
#[inline(always)]
pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> {
if self.len == self.buf.capacity() {
return Err(value);
}
unsafe {
let end = self.as_mut_ptr().add(self.len);
ptr::write(end, value);
self.len += 1;
}
Ok(())
}
--> --------------------
--> maximum size reached
--> --------------------
