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diff --git a/library/alloc/src/vec.rs b/library/alloc/src/vec.rs new file mode 100644 index 00000000000..f5a3d0cd4af --- /dev/null +++ b/library/alloc/src/vec.rs @@ -0,0 +1,3122 @@ +// ignore-tidy-filelength +//! 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<T>`] with [`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; +//! ``` +//! +//! [`Vec<T>`]: ../../std/vec/struct.Vec.html +//! [`new`]: ../../std/vec/struct.Vec.html#method.new +//! [`push`]: ../../std/vec/struct.Vec.html#method.push +//! [`Index`]: ../../std/ops/trait.Index.html +//! [`IndexMut`]: ../../std/ops/trait.IndexMut.html +//! [`vec!`]: ../../std/macro.vec.html + +#![stable(feature = "rust1", since = "1.0.0")] + +use core::cmp::{self, Ordering}; +use core::fmt; +use core::hash::{Hash, Hasher}; +use core::intrinsics::{arith_offset, assume}; +use core::iter::{FromIterator, FusedIterator, TrustedLen}; +use core::marker::PhantomData; +use core::mem::{self, ManuallyDrop}; +use core::ops::Bound::{Excluded, Included, Unbounded}; +use core::ops::{self, Index, IndexMut, RangeBounds}; +use core::ptr::{self, NonNull}; +use core::slice::{self, SliceIndex}; + +use crate::borrow::{Cow, ToOwned}; +use crate::boxed::Box; +use crate::collections::TryReserveError; +use crate::raw_vec::RawVec; + +/// A contiguous growable array type, written `Vec<T>` but pronounced '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 to make initialization more convenient: +/// +/// ``` +/// let mut vec = vec![1, 2, 3]; +/// vec.push(4); +/// assert_eq!(vec, [1, 2, 3, 4]); +/// ``` +/// +/// 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 vec1 = Vec::with_capacity(5); +/// vec1.resize(5, 0); +/// ``` +/// +/// 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. Slices, on the other hand, are read-only objects. +/// To get a 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 x : &[usize] = &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 may 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` may not report a [`capacity`] of 0*. `Vec` will allocate if and only +/// if [`mem::size_of::<T>`]`() * 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`]` - +/// `[`len`] logically uninitialized, contiguous elements. +/// +/// `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`]. +/// +/// [`push`] and [`insert`] will never (re)allocate if the reported capacity is +/// sufficient. [`push`] and [`insert`] *will* (re)allocate if +/// [`len`]` == `[`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)`][`Vec::with_capacity`], will all produce a `Vec` +/// with exactly the requested capacity. If [`len`]` == `[`capacity`], +/// (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 `Vec`. Even if you zero a `Vec`'s memory +/// first, that may 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. +/// +/// `Vec` does not currently guarantee the order in which elements are dropped. +/// The order has changed in the past and may change again. +/// +/// [`vec!`]: ../../std/macro.vec.html +/// [`get`]: ../../std/vec/struct.Vec.html#method.get +/// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut +/// [`Index`]: ../../std/ops/trait.Index.html +/// [`String`]: ../../std/string/struct.String.html +/// [`&str`]: ../../std/primitive.str.html +/// [`Vec::with_capacity`]: ../../std/vec/struct.Vec.html#method.with_capacity +/// [`Vec::new`]: ../../std/vec/struct.Vec.html#method.new +/// [`shrink_to_fit`]: ../../std/vec/struct.Vec.html#method.shrink_to_fit +/// [`capacity`]: ../../std/vec/struct.Vec.html#method.capacity +/// [`mem::size_of::<T>`]: ../../std/mem/fn.size_of.html +/// [`len`]: ../../std/vec/struct.Vec.html#method.len +/// [`push`]: ../../std/vec/struct.Vec.html#method.push +/// [`insert`]: ../../std/vec/struct.Vec.html#method.insert +/// [`reserve`]: ../../std/vec/struct.Vec.html#method.reserve +/// [owned slice]: ../../std/boxed/struct.Box.html +#[stable(feature = "rust1", since = "1.0.0")] +#[cfg_attr(not(test), rustc_diagnostic_item = "vec_type")] +pub struct Vec<T> { + buf: RawVec<T>, + 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] + #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")] + #[stable(feature = "rust1", since = "1.0.0")] + pub const fn new() -> Vec<T> { + Vec { buf: RawVec::NEW, len: 0 } + } + + /// Constructs a new, empty `Vec<T>` with the specified capacity. + /// + /// The vector will be able to hold exactly `capacity` elements without + /// reallocating. If `capacity` is 0, the vector will not allocate. + /// + /// It is important to note that although the returned vector has the + /// *capacity* specified, the vector will have a zero *length*. For an + /// explanation of the difference between length and capacity, see + /// *[Capacity and reallocation]*. + /// + /// [Capacity and reallocation]: #capacity-and-reallocation + /// + /// # 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_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); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn with_capacity(capacity: usize) -> Vec<T> { + Vec { buf: RawVec::with_capacity(capacity), len: 0 } + } + + /// 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`]: #method.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]); + /// ``` + #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")] + pub fn into_raw_parts(self) -> (*mut T, usize, usize) { + let mut me = ManuallyDrop::new(self); + (me.as_mut_ptr(), me.len(), me.capacity()) + } + + /// Creates a `Vec<T>` directly from the raw components of another vector. + /// + /// # Safety + /// + /// This is highly unsafe, due to the number of invariants that aren't + /// checked: + /// + /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>` + /// (at least, it's highly likely to be incorrect if it wasn't). + /// * `T` needs to have the same size and alignment as what `ptr` was allocated with. + /// (`T` having a less strict alignment is not sufficient, the alignment really + /// needs to be equal to satsify the [`dealloc`] requirement that memory must be + /// allocated and deallocated with the same layout.) + /// * `length` needs to be less than or equal to `capacity`. + /// * `capacity` needs to be the capacity that the pointer was allocated with. + /// + /// 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`]: ../../std/string/struct.String.html + /// [`dealloc`]: ../../alloc/alloc/trait.GlobalAlloc.html#tymethod.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 as isize { + /// ptr::write(p.offset(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]); + /// } + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> { + unsafe { Vec { buf: RawVec::from_raw_parts(ptr, capacity), len: length } } + } + + /// Returns the number of elements the vector can hold without + /// reallocating. + /// + /// # Examples + /// + /// ``` + /// let vec: Vec<i32> = Vec::with_capacity(10); + /// assert_eq!(vec.capacity(), 10); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + 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 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); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn reserve(&mut self, additional: usize) { + self.buf.reserve(self.len, additional); + } + + /// Reserves the minimum capacity for exactly `additional` more elements to + /// be inserted in the given `Vec<T>`. 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 overflows `usize`. + /// + /// # Examples + /// + /// ``` + /// let mut vec = vec![1]; + /// vec.reserve_exact(10); + /// assert!(vec.capacity() >= 11); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + 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 avoid + /// frequent reallocations. After calling `reserve`, capacity will be + /// greater than or equal to `self.len() + additional`. Does nothing if + /// capacity is already sufficient. + /// + /// # Errors + /// + /// If the capacity overflows, or the allocator reports a failure, then an error + /// is returned. + /// + /// # Examples + /// + /// ``` + /// #![feature(try_reserve)] + /// 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?"); + /// ``` + #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")] + pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> { + self.buf.try_reserve(self.len, additional) + } + + /// Tries to reserves the minimum capacity for exactly `additional` more elements to + /// be inserted in the given `Vec<T>`. 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. + /// + /// # Errors + /// + /// If the capacity overflows, or the allocator reports a failure, then an error + /// is returned. + /// + /// # Examples + /// + /// ``` + /// #![feature(try_reserve)] + /// 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?"); + /// ``` + #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")] + 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].iter().cloned()); + /// assert_eq!(vec.capacity(), 10); + /// vec.shrink_to_fit(); + /// assert!(vec.capacity() >= 3); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn shrink_to_fit(&mut self) { + 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. + /// + /// # Panics + /// + /// Panics if the current capacity is smaller than the supplied + /// minimum capacity. + /// + /// # Examples + /// + /// ``` + /// #![feature(shrink_to)] + /// let mut vec = Vec::with_capacity(10); + /// vec.extend([1, 2, 3].iter().cloned()); + /// assert_eq!(vec.capacity(), 10); + /// vec.shrink_to(4); + /// assert!(vec.capacity() >= 4); + /// vec.shrink_to(0); + /// assert!(vec.capacity() >= 3); + /// ``` + #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")] + pub fn shrink_to(&mut self, min_capacity: usize) { + self.buf.shrink_to_fit(cmp::max(self.len, min_capacity)); + } + + /// Converts the vector into [`Box<[T]>`][owned slice]. + /// + /// Note that this will drop any excess capacity. + /// + /// [owned slice]: ../../std/boxed/struct.Box.html + /// + /// # 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].iter().cloned()); + /// + /// assert_eq!(vec.capacity(), 10); + /// let slice = vec.into_boxed_slice(); + /// assert_eq!(slice.into_vec().capacity(), 3); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn into_boxed_slice(mut self) -> Box<[T]> { + 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`]: #method.clear + /// [`drain`]: #method.drain + #[stable(feature = "rust1", since = "1.0.0")] + 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 { + 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] + #[stable(feature = "vec_as_slice", since = "1.7.0")] + 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] + #[stable(feature = "vec_as_slice", since = "1.7.0")] + pub fn as_mut_slice(&mut self) -> &mut [T] { + self + } + + /// Returns a raw pointer to the vector's buffer. + /// + /// 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`]: #method.as_mut_ptr + #[stable(feature = "vec_as_ptr", since = "1.37.0")] + #[inline] + 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. + /// + /// 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]); + /// ``` + #[stable(feature = "vec_as_ptr", since = "1.37.0")] + #[inline] + 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 + } + + /// 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`]: #method.truncate + /// [`resize`]: #method.resize + /// [`extend`]: ../../std/iter/trait.Extend.html#tymethod.extend + /// [`clear`]: #method.clear + /// + /// # Safety + /// + /// - `new_len` must be less than or equal to [`capacity()`]. + /// - The elements at `old_len..new_len` must be initialized. + /// + /// [`capacity()`]: #method.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] + #[stable(feature = "rust1", since = "1.0.0")] + 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). + /// + /// # 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] + #[stable(feature = "rust1", since = "1.0.0")] + 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 last = ptr::read(self.as_ptr().add(len - 1)); + let hole = self.as_mut_ptr().add(index); + self.set_len(len - 1); + ptr::replace(hole, last) + } + } + + /// 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]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + 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(); + if index > len { + assert_failed(index, 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); + // Shift everything over to make space. (Duplicating the + // `index`th element into two consecutive places.) + ptr::copy(p, p.offset(1), len - index); + // 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. + /// + /// # 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]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn remove(&mut self, index: usize) -> T { + #[cold] + #[inline(never)] + 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.offset(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` such that `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]); + /// ``` + /// + /// The exact order may be useful for tracking external state, like an index. + /// + /// ``` + /// let mut vec = vec![1, 2, 3, 4, 5]; + /// let keep = [false, true, true, false, true]; + /// let mut i = 0; + /// vec.retain(|_| (keep[i], i += 1).0); + /// assert_eq!(vec, [2, 3, 5]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn retain<F>(&mut self, mut f: F) + where + F: FnMut(&T) -> bool, + { + let len = self.len(); + let mut del = 0; + { + let v = &mut **self; + + for i in 0..len { + if !f(&v[i]) { + del += 1; + } else if del > 0 { + v.swap(i - del, i); + } + } + } + if del > 0 { + self.truncate(len - del); + } + } + + /// 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]); + /// ``` + #[stable(feature = "dedup_by", since = "1.16.0")] + #[inline] + 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"]); + /// ``` + #[stable(feature = "dedup_by", since = "1.16.0")] + pub fn dedup_by<F>(&mut self, same_bucket: F) + where + F: FnMut(&mut T, &mut T) -> bool, + { + let len = { + let (dedup, _) = self.as_mut_slice().partition_dedup_by(same_bucket); + dedup.len() + }; + self.truncate(len); + } + + /// 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]); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + 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.reserve(1); + } + unsafe { + let end = self.as_mut_ptr().add(self.len); + ptr::write(end, value); + self.len += 1; + } + } + + /// Removes the last element from a vector and returns it, or [`None`] if it + /// is empty. + /// + /// [`None`]: ../../std/option/enum.Option.html#variant.None + /// + /// # Examples + /// + /// ``` + /// let mut vec = vec![1, 2, 3]; + /// assert_eq!(vec.pop(), Some(3)); + /// assert_eq!(vec, [1, 2]); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn pop(&mut self) -> Option<T> { + if self.len == 0 { + None + } else { + unsafe { + self.len -= 1; + Some(ptr::read(self.as_ptr().add(self.len()))) + } + } + } + + /// Moves all the elements of `other` into `Self`, leaving `other` empty. + /// + /// # Panics + /// + /// Panics if the number of elements in the vector overflows a `usize`. + /// + /// # 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, []); + /// ``` + #[inline] + #[stable(feature = "append", since = "1.4.0")] + pub fn append(&mut self, other: &mut Self) { + unsafe { + self.append_elements(other.as_slice() as _); + other.set_len(0); + } + } + + /// Appends elements to `Self` from other buffer. + #[inline] + unsafe fn append_elements(&mut self, other: *const [T]) { + let count = unsafe { (*other).len() }; + self.reserve(count); + let len = self.len(); + unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) }; + self.len += count; + } + + /// Creates a draining iterator that removes the specified range in the vector + /// and yields the removed items. + /// + /// When the iterator **is** dropped, all elements in the range are removed + /// from the vector, even if the iterator was not fully consumed. If the + /// iterator **is not** dropped (with [`mem::forget`] for example), it is + /// unspecified how many elements are removed. + /// + /// # 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]; + /// let u: Vec<_> = v.drain(1..).collect(); + /// assert_eq!(v, &[1]); + /// assert_eq!(u, &[2, 3]); + /// + /// // A full range clears the vector + /// v.drain(..); + /// assert_eq!(v, &[]); + /// ``` + #[stable(feature = "drain", since = "1.6.0")] + pub fn drain<R>(&mut self, range: R) -> Drain<'_, T> + where + R: RangeBounds<usize>, + { + // Memory safety + // + // When the Drain is first created, it shortens the length of + // the source vector to make sure no uninitialized or moved-from elements + // are accessible at all if the Drain's destructor never gets to run. + // + // Drain will ptr::read out the values to remove. + // When finished, remaining tail of the vec is copied back to cover + // the hole, and the vector length is restored to the new length. + // + let len = self.len(); + let start = match range.start_bound() { + Included(&n) => n, + Excluded(&n) => n + 1, + Unbounded => 0, + }; + let end = match range.end_bound() { + Included(&n) => n + 1, + Excluded(&n) => n, + Unbounded => len, + }; + + #[cold] + #[inline(never)] + fn start_assert_failed(start: usize, end: usize) -> ! { + panic!("start drain index (is {}) should be <= end drain index (is {})", start, end); + } + + #[cold] + #[inline(never)] + fn end_assert_failed(end: usize, len: usize) -> ! { + panic!("end drain index (is {}) should be <= len (is {})", end, len); + } + + if start > end { + start_assert_failed(start, end); + } + if end > len { + end_assert_failed(end, len); + } + + unsafe { + // set self.vec length's to start, to be safe in case Drain is leaked + self.set_len(start); + // Use the borrow in the IterMut to indicate borrowing behavior of the + // whole Drain iterator (like &mut T). + let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start); + Drain { + tail_start: end, + tail_len: len - end, + iter: range_slice.iter(), + vec: NonNull::from(self), + } + } + } + + /// 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()); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn clear(&mut self) { + self.truncate(0) + } + + /// 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); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn len(&self) -> usize { + self.len + } + + /// 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()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } + + /// 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. + /// + /// # 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]); + /// ``` + #[inline] + #[must_use = "use `.truncate()` if you don't need the other half"] + #[stable(feature = "split_off", since = "1.4.0")] + pub fn split_off(&mut self, at: usize) -> Self { + #[cold] + #[inline(never)] + fn assert_failed(at: usize, len: usize) -> ! { + panic!("`at` split index (is {}) should be <= len (is {})", at, len); + } + + if at > self.len() { + assert_failed(at, self.len()); + } + + let other_len = self.len - at; + let mut other = Vec::with_capacity(other_len); + + // Unsafely `set_len` and copy items to `other`. + unsafe { + self.set_len(at); + other.set_len(other_len); + + ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len()); + } + other + } + + /// 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 [`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]); + /// ``` + /// + /// [`resize`]: #method.resize + /// [`Clone`]: ../../std/clone/trait.Clone.html + #[stable(feature = "vec_resize_with", since = "1.33.0")] + pub fn resize_with<F>(&mut self, new_len: usize, f: F) + where + F: FnMut() -> T, + { + let len = self.len(); + if new_len > len { + self.extend_with(new_len - len, ExtendFunc(f)); + } else { + self.truncate(new_len); + } + } + + /// 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`. + /// + /// This function is similar to the `leak` function on `Box`. + /// + /// 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: + /// + /// ``` + /// #![feature(vec_leak)] + /// + /// let x = vec![1, 2, 3]; + /// let static_ref: &'static mut [usize] = Vec::leak(x); + /// static_ref[0] += 1; + /// assert_eq!(static_ref, &[2, 2, 3]); + /// ``` + #[unstable(feature = "vec_leak", issue = "62195")] + #[inline] + pub fn leak<'a>(vec: Vec<T>) -> &'a mut [T] + where + T: 'a, // Technically not needed, but kept to be explicit. + { + Box::leak(vec.into_boxed_slice()) + } +} + +impl<T: Clone> Vec<T> { + /// 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 [`resize_with`]. + /// + /// # 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]); + /// ``` + /// + /// [`Clone`]: ../../std/clone/trait.Clone.html + /// [`Default`]: ../../std/default/trait.Default.html + /// [`resize_with`]: #method.resize_with + #[stable(feature = "vec_resize", since = "1.5.0")] + pub fn resize(&mut self, new_len: usize, value: T) { + let len = self.len(); + + if new_len > len { + self.extend_with(new_len - len, ExtendElement(value)) + } else { + self.truncate(new_len); + } + } + + /// 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` vector 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]); + /// ``` + /// + /// [`extend`]: #method.extend + #[stable(feature = "vec_extend_from_slice", since = "1.6.0")] + pub fn extend_from_slice(&mut self, other: &[T]) { + self.spec_extend(other.iter()) + } +} + +impl<T: Default> Vec<T> { + /// 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 [`Default::default()`]. + /// If `new_len` is less than `len`, the `Vec` is simply truncated. + /// + /// This method uses [`Default`] to create new values on every push. If + /// you'd rather [`Clone`] a given value, use [`resize`]. + /// + /// # Examples + /// + /// ``` + /// # #![allow(deprecated)] + /// #![feature(vec_resize_default)] + /// + /// let mut vec = vec![1, 2, 3]; + /// vec.resize_default(5); + /// assert_eq!(vec, [1, 2, 3, 0, 0]); + /// + /// let mut vec = vec![1, 2, 3, 4]; + /// vec.resize_default(2); + /// assert_eq!(vec, [1, 2]); + /// ``` + /// + /// [`resize`]: #method.resize + /// [`Default::default()`]: ../../std/default/trait.Default.html#tymethod.default + /// [`Default`]: ../../std/default/trait.Default.html + /// [`Clone`]: ../../std/clone/trait.Clone.html + #[unstable(feature = "vec_resize_default", issue = "41758")] + #[rustc_deprecated( + reason = "This is moving towards being removed in favor \ + of `.resize_with(Default::default)`. If you disagree, please comment \ + in the tracking issue.", + since = "1.33.0" + )] + pub fn resize_default(&mut self, new_len: usize) { + let len = self.len(); + + if new_len > len { + self.extend_with(new_len - len, ExtendDefault); + } else { + self.truncate(new_len); + } + } +} + +// This code generalizes `extend_with_{element,default}`. +trait ExtendWith<T> { + fn next(&mut self) -> T; + fn last(self) -> T; +} + +struct ExtendElement<T>(T); +impl<T: Clone> ExtendWith<T> for ExtendElement<T> { + fn next(&mut self) -> T { + self.0.clone() + } + fn last(self) -> T { + self.0 + } +} + +struct ExtendDefault; +impl<T: Default> ExtendWith<T> for ExtendDefault { + fn next(&mut self) -> T { + Default::default() + } + fn last(self) -> T { + Default::default() + } +} + +struct ExtendFunc<F>(F); +impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> { + fn next(&mut self) -> T { + (self.0)() + } + fn last(mut self) -> T { + (self.0)() + } +} + +impl<T> Vec<T> { + /// Extend the vector by `n` values, using the given generator. + fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) { + self.reserve(n); + + unsafe { + let mut ptr = self.as_mut_ptr().add(self.len()); + // Use SetLenOnDrop to work around bug where compiler + // may not realize the store through `ptr` through self.set_len() + // don't alias. + let mut local_len = SetLenOnDrop::new(&mut self.len); + + // Write all elements except the last one + for _ in 1..n { + ptr::write(ptr, value.next()); + ptr = ptr.offset(1); + // Increment the length in every step in case next() panics + local_len.increment_len(1); + } + + if n > 0 { + // We can write the last element directly without cloning needlessly + ptr::write(ptr, value.last()); + local_len.increment_len(1); + } + + // len set by scope guard + } + } +} + +// Set the length of the vec when the `SetLenOnDrop` value goes out of scope. +// +// The idea is: The length field in SetLenOnDrop is a local variable +// that the optimizer will see does not alias with any stores through the Vec's data +// pointer. This is a workaround for alias analysis issue #32155 +struct SetLenOnDrop<'a> { + len: &'a mut usize, + local_len: usize, +} + +impl<'a> SetLenOnDrop<'a> { + #[inline] + fn new(len: &'a mut usize) -> Self { + SetLenOnDrop { local_len: *len, len } + } + + #[inline] + fn increment_len(&mut self, increment: usize) { + self.local_len += increment; + } +} + +impl Drop for SetLenOnDrop<'_> { + #[inline] + fn drop(&mut self) { + *self.len = self.local_len; + } +} + +impl<T: PartialEq> Vec<T> { + /// 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]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn dedup(&mut self) { + self.dedup_by(|a, b| a == b) + } +} + +impl<T> Vec<T> { + /// Removes the first instance of `item` from the vector if the item exists. + /// + /// This method will be removed soon. + #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")] + #[rustc_deprecated( + reason = "Removing the first item equal to a needle is already easily possible \ + with iterators and the current Vec methods. Furthermore, having a method for \ + one particular case of removal (linear search, only the first item, no swap remove) \ + but not for others is inconsistent. This method will be removed soon.", + since = "1.46.0" + )] + pub fn remove_item<V>(&mut self, item: &V) -> Option<T> + where + T: PartialEq<V>, + { + let pos = self.iter().position(|x| *x == *item)?; + Some(self.remove(pos)) + } +} + +//////////////////////////////////////////////////////////////////////////////// +// Internal methods and functions +//////////////////////////////////////////////////////////////////////////////// + +#[doc(hidden)] +#[stable(feature = "rust1", since = "1.0.0")] +pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> { + <T as SpecFromElem>::from_elem(elem, n) +} + +// Specialization trait used for Vec::from_elem +trait SpecFromElem: Sized { + fn from_elem(elem: Self, n: usize) -> Vec<Self>; +} + +impl<T: Clone> SpecFromElem for T { + default fn from_elem(elem: Self, n: usize) -> Vec<Self> { + let mut v = Vec::with_capacity(n); + v.extend_with(n, ExtendElement(elem)); + v + } +} + +impl SpecFromElem for i8 { + #[inline] + fn from_elem(elem: i8, n: usize) -> Vec<i8> { + if elem == 0 { + return Vec { buf: RawVec::with_capacity_zeroed(n), len: n }; + } + unsafe { + let mut v = Vec::with_capacity(n); + ptr::write_bytes(v.as_mut_ptr(), elem as u8, n); + v.set_len(n); + v + } + } +} + +impl SpecFromElem for u8 { + #[inline] + fn from_elem(elem: u8, n: usize) -> Vec<u8> { + if elem == 0 { + return Vec { buf: RawVec::with_capacity_zeroed(n), len: n }; + } + unsafe { + let mut v = Vec::with_capacity(n); + ptr::write_bytes(v.as_mut_ptr(), elem, n); + v.set_len(n); + v + } + } +} + +impl<T: Clone + IsZero> SpecFromElem for T { + #[inline] + fn from_elem(elem: T, n: usize) -> Vec<T> { + if elem.is_zero() { + return Vec { buf: RawVec::with_capacity_zeroed(n), len: n }; + } + let mut v = Vec::with_capacity(n); + v.extend_with(n, ExtendElement(elem)); + v + } +} + +#[rustc_specialization_trait] +unsafe trait IsZero { + /// Whether this value is zero + fn is_zero(&self) -> bool; +} + +macro_rules! impl_is_zero { + ($t:ty, $is_zero:expr) => { + unsafe impl IsZero for $t { + #[inline] + fn is_zero(&self) -> bool { + $is_zero(*self) + } + } + }; +} + +impl_is_zero!(i16, |x| x == 0); +impl_is_zero!(i32, |x| x == 0); +impl_is_zero!(i64, |x| x == 0); +impl_is_zero!(i128, |x| x == 0); +impl_is_zero!(isize, |x| x == 0); + +impl_is_zero!(u16, |x| x == 0); +impl_is_zero!(u32, |x| x == 0); +impl_is_zero!(u64, |x| x == 0); +impl_is_zero!(u128, |x| x == 0); +impl_is_zero!(usize, |x| x == 0); + +impl_is_zero!(bool, |x| x == false); +impl_is_zero!(char, |x| x == '\0'); + +impl_is_zero!(f32, |x: f32| x.to_bits() == 0); +impl_is_zero!(f64, |x: f64| x.to_bits() == 0); + +unsafe impl<T> IsZero for *const T { + #[inline] + fn is_zero(&self) -> bool { + (*self).is_null() + } +} + +unsafe impl<T> IsZero for *mut T { + #[inline] + fn is_zero(&self) -> bool { + (*self).is_null() + } +} + +// `Option<&T>` and `Option<Box<T>>` are guaranteed to represent `None` as null. +// For fat pointers, the bytes that would be the pointer metadata in the `Some` +// variant are padding in the `None` variant, so ignoring them and +// zero-initializing instead is ok. +// `Option<&mut T>` never implements `Clone`, so there's no need for an impl of +// `SpecFromElem`. + +unsafe impl<T: ?Sized> IsZero for Option<&T> { + #[inline] + fn is_zero(&self) -> bool { + self.is_none() + } +} + +unsafe impl<T: ?Sized> IsZero for Option<Box<T>> { + #[inline] + fn is_zero(&self) -> bool { + self.is_none() + } +} + +//////////////////////////////////////////////////////////////////////////////// +// Common trait implementations for Vec +//////////////////////////////////////////////////////////////////////////////// + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> ops::Deref for Vec<T> { + type Target = [T]; + + fn deref(&self) -> &[T] { + unsafe { slice::from_raw_parts(self.as_ptr(), self.len) } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> ops::DerefMut for Vec<T> { + fn deref_mut(&mut self) -> &mut [T] { + unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Clone> Clone for Vec<T> { + #[cfg(not(test))] + fn clone(&self) -> Vec<T> { + <[T]>::to_vec(&**self) + } + + // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is + // required for this method definition, is not available. Instead use the + // `slice::to_vec` function which is only available with cfg(test) + // NB see the slice::hack module in slice.rs for more information + #[cfg(test)] + fn clone(&self) -> Vec<T> { + crate::slice::to_vec(&**self) + } + + fn clone_from(&mut self, other: &Vec<T>) { + other.as_slice().clone_into(self); + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Hash> Hash for Vec<T> { + #[inline] + fn hash<H: Hasher>(&self, state: &mut H) { + Hash::hash(&**self, state) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_on_unimplemented( + message = "vector indices are of type `usize` or ranges of `usize`", + label = "vector indices are of type `usize` or ranges of `usize`" +)] +impl<T, I: SliceIndex<[T]>> Index<I> for Vec<T> { + type Output = I::Output; + + #[inline] + fn index(&self, index: I) -> &Self::Output { + Index::index(&**self, index) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_on_unimplemented( + message = "vector indices are of type `usize` or ranges of `usize`", + label = "vector indices are of type `usize` or ranges of `usize`" +)] +impl<T, I: SliceIndex<[T]>> IndexMut<I> for Vec<T> { + #[inline] + fn index_mut(&mut self, index: I) -> &mut Self::Output { + IndexMut::index_mut(&mut **self, index) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> FromIterator<T> for Vec<T> { + #[inline] + fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> { + <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter()) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> IntoIterator for Vec<T> { + type Item = T; + type IntoIter = IntoIter<T>; + + /// 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()]; + /// for s in v.into_iter() { + /// // s has type String, not &String + /// println!("{}", s); + /// } + /// ``` + #[inline] + fn into_iter(self) -> IntoIter<T> { + unsafe { + let mut me = ManuallyDrop::new(self); + let begin = me.as_mut_ptr(); + let end = if mem::size_of::<T>() == 0 { + arith_offset(begin as *const i8, me.len() as isize) as *const T + } else { + begin.add(me.len()) as *const T + }; + let cap = me.buf.capacity(); + IntoIter { + buf: NonNull::new_unchecked(begin), + phantom: PhantomData, + cap, + ptr: begin, + end, + } + } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> IntoIterator for &'a Vec<T> { + type Item = &'a T; + type IntoIter = slice::Iter<'a, T>; + + fn into_iter(self) -> slice::Iter<'a, T> { + self.iter() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> IntoIterator for &'a mut Vec<T> { + type Item = &'a mut T; + type IntoIter = slice::IterMut<'a, T>; + + fn into_iter(self) -> slice::IterMut<'a, T> { + self.iter_mut() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Extend<T> for Vec<T> { + #[inline] + fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) { + <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter()) + } + + #[inline] + fn extend_one(&mut self, item: T) { + self.push(item); + } + + #[inline] + fn extend_reserve(&mut self, additional: usize) { + self.reserve(additional); + } +} + +// Specialization trait used for Vec::from_iter and Vec::extend +trait SpecExtend<T, I> { + fn from_iter(iter: I) -> Self; + fn spec_extend(&mut self, iter: I); +} + +impl<T, I> SpecExtend<T, I> for Vec<T> +where + I: Iterator<Item = T>, +{ + default fn from_iter(mut iterator: I) -> Self { + // Unroll the first iteration, as the vector is going to be + // expanded on this iteration in every case when the iterable is not + // empty, but the loop in extend_desugared() is not going to see the + // vector being full in the few subsequent loop iterations. + // So we get better branch prediction. + let mut vector = match iterator.next() { + None => return Vec::new(), + Some(element) => { + let (lower, _) = iterator.size_hint(); + let mut vector = Vec::with_capacity(lower.saturating_add(1)); + unsafe { + ptr::write(vector.as_mut_ptr(), element); + vector.set_len(1); + } + vector + } + }; + <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator); + vector + } + + default fn spec_extend(&mut self, iter: I) { + self.extend_desugared(iter) + } +} + +impl<T, I> SpecExtend<T, I> for Vec<T> +where + I: TrustedLen<Item = T>, +{ + default fn from_iter(iterator: I) -> Self { + let mut vector = Vec::new(); + vector.spec_extend(iterator); + vector + } + + default fn spec_extend(&mut self, iterator: I) { + // This is the case for a TrustedLen iterator. + let (low, high) = iterator.size_hint(); + if let Some(high_value) = high { + debug_assert_eq!( + low, + high_value, + "TrustedLen iterator's size hint is not exact: {:?}", + (low, high) + ); + } + if let Some(additional) = high { + self.reserve(additional); + unsafe { + let mut ptr = self.as_mut_ptr().add(self.len()); + let mut local_len = SetLenOnDrop::new(&mut self.len); + iterator.for_each(move |element| { + ptr::write(ptr, element); + ptr = ptr.offset(1); + // NB can't overflow since we would have had to alloc the address space + local_len.increment_len(1); + }); + } + } else { + self.extend_desugared(iterator) + } + } +} + +impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> { + fn from_iter(iterator: IntoIter<T>) -> Self { + // A common case is passing a vector into a function which immediately + // re-collects into a vector. We can short circuit this if the IntoIter + // has not been advanced at all. + if iterator.buf.as_ptr() as *const _ == iterator.ptr { + unsafe { + let it = ManuallyDrop::new(iterator); + Vec::from_raw_parts(it.buf.as_ptr(), it.len(), it.cap) + } + } else { + let mut vector = Vec::new(); + vector.spec_extend(iterator); + vector + } + } + + fn spec_extend(&mut self, mut iterator: IntoIter<T>) { + unsafe { + self.append_elements(iterator.as_slice() as _); + } + iterator.ptr = iterator.end; + } +} + +impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T> +where + I: Iterator<Item = &'a T>, + T: Clone, +{ + default fn from_iter(iterator: I) -> Self { + SpecExtend::from_iter(iterator.cloned()) + } + + default fn spec_extend(&mut self, iterator: I) { + self.spec_extend(iterator.cloned()) + } +} + +impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T> +where + T: Copy, +{ + fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) { + let slice = iterator.as_slice(); + self.reserve(slice.len()); + unsafe { + let len = self.len(); + let dst_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(len), slice.len()); + dst_slice.copy_from_slice(slice); + self.set_len(len + slice.len()); + } + } +} + +impl<T> Vec<T> { + fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) { + // This is the case for a general iterator. + // + // This function should be the moral equivalent of: + // + // for item in iterator { + // self.push(item); + // } + while let Some(element) = iterator.next() { + let len = self.len(); + if len == self.capacity() { + let (lower, _) = iterator.size_hint(); + self.reserve(lower.saturating_add(1)); + } + unsafe { + ptr::write(self.as_mut_ptr().add(len), element); + // NB can't overflow since we would have had to alloc the address space + self.set_len(len + 1); + } + } + } + + /// 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`. + /// + /// The element 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 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]; + /// let new = [7, 8]; + /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect(); + /// assert_eq!(v, &[7, 8, 3]); + /// assert_eq!(u, &[1, 2]); + /// ``` + #[inline] + #[stable(feature = "vec_splice", since = "1.21.0")] + pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter> + where + R: RangeBounds<usize>, + I: IntoIterator<Item = T>, + { + Splice { drain: self.drain(range), replace_with: replace_with.into_iter() } + } + + /// 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. + /// + /// Using this method is equivalent to the following code: + /// + /// ``` + /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 }; + /// # let mut vec = vec![1, 2, 3, 4, 5, 6]; + /// let mut i = 0; + /// while i != vec.len() { + /// if some_predicate(&mut vec[i]) { + /// let val = vec.remove(i); + /// // your code here + /// } else { + /// i += 1; + /// } + /// } + /// + /// # assert_eq!(vec, vec![1, 4, 5]); + /// ``` + /// + /// But `drain_filter` is easier to use. `drain_filter` is also more efficient, + /// because it can backshift the elements of the array in bulk. + /// + /// Note that `drain_filter` 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(drain_filter)] + /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15]; + /// + /// let evens = numbers.drain_filter(|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]); + /// ``` + #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")] + pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F> + where + F: FnMut(&mut T) -> bool, + { + let old_len = self.len(); + + // Guard against us getting leaked (leak amplification) + unsafe { + self.set_len(0); + } + + DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false } + } +} + +/// 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. +/// +/// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice +#[stable(feature = "extend_ref", since = "1.2.0")] +impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> { + fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) { + self.spec_extend(iter.into_iter()) + } + + #[inline] + fn extend_one(&mut self, &item: &'a T) { + self.push(item); + } + + #[inline] + fn extend_reserve(&mut self, additional: usize) { + self.reserve(additional); + } +} + +macro_rules! __impl_slice_eq1 { + ([$($vars:tt)*] $lhs:ty, $rhs:ty $(where $ty:ty: $bound:ident)?, #[$stability:meta]) => { + #[$stability] + impl<A, B, $($vars)*> PartialEq<$rhs> for $lhs + where + A: PartialEq<B>, + $($ty: $bound)? + { + #[inline] + fn eq(&self, other: &$rhs) -> bool { self[..] == other[..] } + #[inline] + fn ne(&self, other: &$rhs) -> bool { self[..] != other[..] } + } + } +} + +__impl_slice_eq1! { [] Vec<A>, Vec<B>, #[stable(feature = "rust1", since = "1.0.0")] } +__impl_slice_eq1! { [] Vec<A>, &[B], #[stable(feature = "rust1", since = "1.0.0")] } +__impl_slice_eq1! { [] Vec<A>, &mut [B], #[stable(feature = "rust1", since = "1.0.0")] } +__impl_slice_eq1! { [] &[A], Vec<B>, #[stable(feature = "partialeq_vec_for_ref_slice", since = "1.46.0")] } +__impl_slice_eq1! { [] &mut [A], Vec<B>, #[stable(feature = "partialeq_vec_for_ref_slice", since = "1.46.0")] } +__impl_slice_eq1! { [] Cow<'_, [A]>, Vec<B> where A: Clone, #[stable(feature = "rust1", since = "1.0.0")] } +__impl_slice_eq1! { [] Cow<'_, [A]>, &[B] where A: Clone, #[stable(feature = "rust1", since = "1.0.0")] } +__impl_slice_eq1! { [] Cow<'_, [A]>, &mut [B] where A: Clone, #[stable(feature = "rust1", since = "1.0.0")] } +__impl_slice_eq1! { [const N: usize] Vec<A>, [B; N], #[stable(feature = "rust1", since = "1.0.0")] } +__impl_slice_eq1! { [const N: usize] Vec<A>, &[B; N], #[stable(feature = "rust1", since = "1.0.0")] } + +// NOTE: some less important impls are omitted to reduce code bloat +// FIXME(Centril): Reconsider this? +//__impl_slice_eq1! { [const N: usize] Vec<A>, &mut [B; N], } +//__impl_slice_eq1! { [const N: usize] [A; N], Vec<B>, } +//__impl_slice_eq1! { [const N: usize] &[A; N], Vec<B>, } +//__impl_slice_eq1! { [const N: usize] &mut [A; N], Vec<B>, } +//__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, [B; N], } +//__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &[B; N], } +//__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &mut [B; N], } + +/// Implements comparison of vectors, lexicographically. +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: PartialOrd> PartialOrd for Vec<T> { + #[inline] + fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> { + PartialOrd::partial_cmp(&**self, &**other) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Eq> Eq for Vec<T> {} + +/// Implements ordering of vectors, lexicographically. +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Ord> Ord for Vec<T> { + #[inline] + fn cmp(&self, other: &Vec<T>) -> Ordering { + Ord::cmp(&**self, &**other) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<#[may_dangle] T> Drop for Vec<T> { + fn drop(&mut self) { + unsafe { + // use drop for [T] + // use a raw slice to refer to the elements of the vector as weakest necessary type; + // could avoid questions of validity in certain cases + ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len)) + } + // RawVec handles deallocation + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Default for Vec<T> { + /// Creates an empty `Vec<T>`. + fn default() -> Vec<T> { + Vec::new() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: fmt::Debug> fmt::Debug for Vec<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Debug::fmt(&**self, f) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> AsRef<Vec<T>> for Vec<T> { + fn as_ref(&self) -> &Vec<T> { + self + } +} + +#[stable(feature = "vec_as_mut", since = "1.5.0")] +impl<T> AsMut<Vec<T>> for Vec<T> { + fn as_mut(&mut self) -> &mut Vec<T> { + self + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> AsRef<[T]> for Vec<T> { + fn as_ref(&self) -> &[T] { + self + } +} + +#[stable(feature = "vec_as_mut", since = "1.5.0")] +impl<T> AsMut<[T]> for Vec<T> { + fn as_mut(&mut self) -> &mut [T] { + self + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Clone> From<&[T]> for Vec<T> { + #[cfg(not(test))] + fn from(s: &[T]) -> Vec<T> { + s.to_vec() + } + #[cfg(test)] + fn from(s: &[T]) -> Vec<T> { + crate::slice::to_vec(s) + } +} + +#[stable(feature = "vec_from_mut", since = "1.19.0")] +impl<T: Clone> From<&mut [T]> for Vec<T> { + #[cfg(not(test))] + fn from(s: &mut [T]) -> Vec<T> { + s.to_vec() + } + #[cfg(test)] + fn from(s: &mut [T]) -> Vec<T> { + crate::slice::to_vec(s) + } +} + +#[stable(feature = "vec_from_array", since = "1.44.0")] +impl<T, const N: usize> From<[T; N]> for Vec<T> { + #[cfg(not(test))] + fn from(s: [T; N]) -> Vec<T> { + <[T]>::into_vec(box s) + } + #[cfg(test)] + fn from(s: [T; N]) -> Vec<T> { + crate::slice::into_vec(box s) + } +} + +#[stable(feature = "vec_from_cow_slice", since = "1.14.0")] +impl<'a, T> From<Cow<'a, [T]>> for Vec<T> +where + [T]: ToOwned<Owned = Vec<T>>, +{ + fn from(s: Cow<'a, [T]>) -> Vec<T> { + s.into_owned() + } +} + +// note: test pulls in libstd, which causes errors here +#[cfg(not(test))] +#[stable(feature = "vec_from_box", since = "1.18.0")] +impl<T> From<Box<[T]>> for Vec<T> { + fn from(s: Box<[T]>) -> Vec<T> { + s.into_vec() + } +} + +// note: test pulls in libstd, which causes errors here +#[cfg(not(test))] +#[stable(feature = "box_from_vec", since = "1.20.0")] +impl<T> From<Vec<T>> for Box<[T]> { + fn from(v: Vec<T>) -> Box<[T]> { + v.into_boxed_slice() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl From<&str> for Vec<u8> { + fn from(s: &str) -> Vec<u8> { + From::from(s.as_bytes()) + } +} + +//////////////////////////////////////////////////////////////////////////////// +// Clone-on-write +//////////////////////////////////////////////////////////////////////////////// + +#[stable(feature = "cow_from_vec", since = "1.8.0")] +impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> { + fn from(s: &'a [T]) -> Cow<'a, [T]> { + Cow::Borrowed(s) + } +} + +#[stable(feature = "cow_from_vec", since = "1.8.0")] +impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> { + fn from(v: Vec<T>) -> Cow<'a, [T]> { + Cow::Owned(v) + } +} + +#[stable(feature = "cow_from_vec_ref", since = "1.28.0")] +impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> { + fn from(v: &'a Vec<T>) -> Cow<'a, [T]> { + Cow::Borrowed(v.as_slice()) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> FromIterator<T> for Cow<'a, [T]> +where + T: Clone, +{ + fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> { + Cow::Owned(FromIterator::from_iter(it)) + } +} + +//////////////////////////////////////////////////////////////////////////////// +// Iterators +//////////////////////////////////////////////////////////////////////////////// + +/// An iterator that moves out of a vector. +/// +/// This `struct` is created by the `into_iter` method on [`Vec`] (provided +/// by the [`IntoIterator`] trait). +/// +/// [`Vec`]: struct.Vec.html +/// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html +#[stable(feature = "rust1", since = "1.0.0")] +pub struct IntoIter<T> { + buf: NonNull<T>, + phantom: PhantomData<T>, + cap: usize, + ptr: *const T, + end: *const T, +} + +#[stable(feature = "vec_intoiter_debug", since = "1.13.0")] +impl<T: fmt::Debug> fmt::Debug for IntoIter<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("IntoIter").field(&self.as_slice()).finish() + } +} + +impl<T> IntoIter<T> { + /// Returns the remaining items of this iterator as a slice. + /// + /// # Examples + /// + /// ``` + /// let vec = vec!['a', 'b', 'c']; + /// let mut into_iter = vec.into_iter(); + /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']); + /// let _ = into_iter.next().unwrap(); + /// assert_eq!(into_iter.as_slice(), &['b', 'c']); + /// ``` + #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")] + pub fn as_slice(&self) -> &[T] { + unsafe { slice::from_raw_parts(self.ptr, self.len()) } + } + + /// Returns the remaining items of this iterator as a mutable slice. + /// + /// # Examples + /// + /// ``` + /// let vec = vec!['a', 'b', 'c']; + /// let mut into_iter = vec.into_iter(); + /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']); + /// into_iter.as_mut_slice()[2] = 'z'; + /// assert_eq!(into_iter.next().unwrap(), 'a'); + /// assert_eq!(into_iter.next().unwrap(), 'b'); + /// assert_eq!(into_iter.next().unwrap(), 'z'); + /// ``` + #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")] + pub fn as_mut_slice(&mut self) -> &mut [T] { + unsafe { &mut *self.as_raw_mut_slice() } + } + + fn as_raw_mut_slice(&mut self) -> *mut [T] { + ptr::slice_from_raw_parts_mut(self.ptr as *mut T, self.len()) + } +} + +#[stable(feature = "vec_intoiter_as_ref", since = "1.46.0")] +impl<T> AsRef<[T]> for IntoIter<T> { + fn as_ref(&self) -> &[T] { + self.as_slice() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<T: Send> Send for IntoIter<T> {} +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<T: Sync> Sync for IntoIter<T> {} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Iterator for IntoIter<T> { + type Item = T; + + #[inline] + fn next(&mut self) -> Option<T> { + unsafe { + if self.ptr as *const _ == self.end { + None + } else { + if mem::size_of::<T>() == 0 { + // purposefully don't use 'ptr.offset' because for + // vectors with 0-size elements this would return the + // same pointer. + self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T; + + // Make up a value of this ZST. + Some(mem::zeroed()) + } else { + let old = self.ptr; + self.ptr = self.ptr.offset(1); + + Some(ptr::read(old)) + } + } + } + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + let exact = if mem::size_of::<T>() == 0 { + (self.end as usize).wrapping_sub(self.ptr as usize) + } else { + unsafe { self.end.offset_from(self.ptr) as usize } + }; + (exact, Some(exact)) + } + + #[inline] + fn count(self) -> usize { + self.len() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> DoubleEndedIterator for IntoIter<T> { + #[inline] + fn next_back(&mut self) -> Option<T> { + unsafe { + if self.end == self.ptr { + None + } else { + if mem::size_of::<T>() == 0 { + // See above for why 'ptr.offset' isn't used + self.end = arith_offset(self.end as *const i8, -1) as *mut T; + + // Make up a value of this ZST. + Some(mem::zeroed()) + } else { + self.end = self.end.offset(-1); + + Some(ptr::read(self.end)) + } + } + } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> ExactSizeIterator for IntoIter<T> { + fn is_empty(&self) -> bool { + self.ptr == self.end + } +} + +#[stable(feature = "fused", since = "1.26.0")] +impl<T> FusedIterator for IntoIter<T> {} + +#[unstable(feature = "trusted_len", issue = "37572")] +unsafe impl<T> TrustedLen for IntoIter<T> {} + +#[stable(feature = "vec_into_iter_clone", since = "1.8.0")] +impl<T: Clone> Clone for IntoIter<T> { + fn clone(&self) -> IntoIter<T> { + self.as_slice().to_owned().into_iter() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<#[may_dangle] T> Drop for IntoIter<T> { + fn drop(&mut self) { + struct DropGuard<'a, T>(&'a mut IntoIter<T>); + + impl<T> Drop for DropGuard<'_, T> { + fn drop(&mut self) { + // RawVec handles deallocation + let _ = unsafe { RawVec::from_raw_parts(self.0.buf.as_ptr(), self.0.cap) }; + } + } + + let guard = DropGuard(self); + // destroy the remaining elements + unsafe { + ptr::drop_in_place(guard.0.as_raw_mut_slice()); + } + // now `guard` will be dropped and do the rest + } +} + +/// A draining iterator for `Vec<T>`. +/// +/// This `struct` is created by the [`drain`] method on [`Vec`]. +/// +/// [`drain`]: struct.Vec.html#method.drain +/// [`Vec`]: struct.Vec.html +#[stable(feature = "drain", since = "1.6.0")] +pub struct Drain<'a, T: 'a> { + /// Index of tail to preserve + tail_start: usize, + /// Length of tail + tail_len: usize, + /// Current remaining range to remove + iter: slice::Iter<'a, T>, + vec: NonNull<Vec<T>>, +} + +#[stable(feature = "collection_debug", since = "1.17.0")] +impl<T: fmt::Debug> fmt::Debug for Drain<'_, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("Drain").field(&self.iter.as_slice()).finish() + } +} + +impl<'a, T> Drain<'a, T> { + /// Returns the remaining items of this iterator as a slice. + /// + /// # Examples + /// + /// ``` + /// let mut vec = vec!['a', 'b', 'c']; + /// let mut drain = vec.drain(..); + /// assert_eq!(drain.as_slice(), &['a', 'b', 'c']); + /// let _ = drain.next().unwrap(); + /// assert_eq!(drain.as_slice(), &['b', 'c']); + /// ``` + #[stable(feature = "vec_drain_as_slice", since = "1.46.0")] + pub fn as_slice(&self) -> &[T] { + self.iter.as_slice() + } +} + +#[stable(feature = "vec_drain_as_slice", since = "1.46.0")] +impl<'a, T> AsRef<[T]> for Drain<'a, T> { + fn as_ref(&self) -> &[T] { + self.as_slice() + } +} + +#[stable(feature = "drain", since = "1.6.0")] +unsafe impl<T: Sync> Sync for Drain<'_, T> {} +#[stable(feature = "drain", since = "1.6.0")] +unsafe impl<T: Send> Send for Drain<'_, T> {} + +#[stable(feature = "drain", since = "1.6.0")] +impl<T> Iterator for Drain<'_, T> { + type Item = T; + + #[inline] + fn next(&mut self) -> Option<T> { + self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) }) + } + + fn size_hint(&self) -> (usize, Option<usize>) { + self.iter.size_hint() + } +} + +#[stable(feature = "drain", since = "1.6.0")] +impl<T> DoubleEndedIterator for Drain<'_, T> { + #[inline] + fn next_back(&mut self) -> Option<T> { + self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) }) + } +} + +#[stable(feature = "drain", since = "1.6.0")] +impl<T> Drop for Drain<'_, T> { + fn drop(&mut self) { + /// Continues dropping the remaining elements in the `Drain`, then moves back the + /// un-`Drain`ed elements to restore the original `Vec`. + struct DropGuard<'r, 'a, T>(&'r mut Drain<'a, T>); + + impl<'r, 'a, T> Drop for DropGuard<'r, 'a, T> { + fn drop(&mut self) { + // Continue the same loop we have below. If the loop already finished, this does + // nothing. + self.0.for_each(drop); + + if self.0.tail_len > 0 { + unsafe { + let source_vec = self.0.vec.as_mut(); + // memmove back untouched tail, update to new length + let start = source_vec.len(); + let tail = self.0.tail_start; + if tail != start { + let src = source_vec.as_ptr().add(tail); + let dst = source_vec.as_mut_ptr().add(start); + ptr::copy(src, dst, self.0.tail_len); + } + source_vec.set_len(start + self.0.tail_len); + } + } + } + } + + // exhaust self first + while let Some(item) = self.next() { + let guard = DropGuard(self); + drop(item); + mem::forget(guard); + } + + // Drop a `DropGuard` to move back the non-drained tail of `self`. + DropGuard(self); + } +} + +#[stable(feature = "drain", since = "1.6.0")] +impl<T> ExactSizeIterator for Drain<'_, T> { + fn is_empty(&self) -> bool { + self.iter.is_empty() + } +} + +#[unstable(feature = "trusted_len", issue = "37572")] +unsafe impl<T> TrustedLen for Drain<'_, T> {} + +#[stable(feature = "fused", since = "1.26.0")] +impl<T> FusedIterator for Drain<'_, T> {} + +/// A splicing iterator for `Vec`. +/// +/// This struct is created by the [`splice()`] method on [`Vec`]. See its +/// documentation for more. +/// +/// [`splice()`]: struct.Vec.html#method.splice +/// [`Vec`]: struct.Vec.html +#[derive(Debug)] +#[stable(feature = "vec_splice", since = "1.21.0")] +pub struct Splice<'a, I: Iterator + 'a> { + drain: Drain<'a, I::Item>, + replace_with: I, +} + +#[stable(feature = "vec_splice", since = "1.21.0")] +impl<I: Iterator> Iterator for Splice<'_, I> { + type Item = I::Item; + + fn next(&mut self) -> Option<Self::Item> { + self.drain.next() + } + + fn size_hint(&self) -> (usize, Option<usize>) { + self.drain.size_hint() + } +} + +#[stable(feature = "vec_splice", since = "1.21.0")] +impl<I: Iterator> DoubleEndedIterator for Splice<'_, I> { + fn next_back(&mut self) -> Option<Self::Item> { + self.drain.next_back() + } +} + +#[stable(feature = "vec_splice", since = "1.21.0")] +impl<I: Iterator> ExactSizeIterator for Splice<'_, I> {} + +#[stable(feature = "vec_splice", since = "1.21.0")] +impl<I: Iterator> Drop for Splice<'_, I> { + fn drop(&mut self) { + self.drain.by_ref().for_each(drop); + + unsafe { + if self.drain.tail_len == 0 { + self.drain.vec.as_mut().extend(self.replace_with.by_ref()); + return; + } + + // First fill the range left by drain(). + if !self.drain.fill(&mut self.replace_with) { + return; + } + + // There may be more elements. Use the lower bound as an estimate. + // FIXME: Is the upper bound a better guess? Or something else? + let (lower_bound, _upper_bound) = self.replace_with.size_hint(); + if lower_bound > 0 { + self.drain.move_tail(lower_bound); + if !self.drain.fill(&mut self.replace_with) { + return; + } + } + + // Collect any remaining elements. + // This is a zero-length vector which does not allocate if `lower_bound` was exact. + let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter(); + // Now we have an exact count. + if collected.len() > 0 { + self.drain.move_tail(collected.len()); + let filled = self.drain.fill(&mut collected); + debug_assert!(filled); + debug_assert_eq!(collected.len(), 0); + } + } + // Let `Drain::drop` move the tail back if necessary and restore `vec.len`. + } +} + +/// Private helper methods for `Splice::drop` +impl<T> Drain<'_, T> { + /// The range from `self.vec.len` to `self.tail_start` contains elements + /// that have been moved out. + /// Fill that range as much as possible with new elements from the `replace_with` iterator. + /// Returns `true` if we filled the entire range. (`replace_with.next()` didn’t return `None`.) + unsafe fn fill<I: Iterator<Item = T>>(&mut self, replace_with: &mut I) -> bool { + let vec = unsafe { self.vec.as_mut() }; + let range_start = vec.len; + let range_end = self.tail_start; + let range_slice = unsafe { + slice::from_raw_parts_mut(vec.as_mut_ptr().add(range_start), range_end - range_start) + }; + + for place in range_slice { + if let Some(new_item) = replace_with.next() { + unsafe { ptr::write(place, new_item) }; + vec.len += 1; + } else { + return false; + } + } + true + } + + /// Makes room for inserting more elements before the tail. + unsafe fn move_tail(&mut self, additional: usize) { + let vec = unsafe { self.vec.as_mut() }; + let len = self.tail_start + self.tail_len; + vec.buf.reserve(len, additional); + + let new_tail_start = self.tail_start + additional; + unsafe { + let src = vec.as_ptr().add(self.tail_start); + let dst = vec.as_mut_ptr().add(new_tail_start); + ptr::copy(src, dst, self.tail_len); + } + self.tail_start = new_tail_start; + } +} + +/// An iterator produced by calling `drain_filter` on Vec. +#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")] +#[derive(Debug)] +pub struct DrainFilter<'a, T, F> +where + F: FnMut(&mut T) -> bool, +{ + vec: &'a mut Vec<T>, + /// The index of the item that will be inspected by the next call to `next`. + idx: usize, + /// The number of items that have been drained (removed) thus far. + del: usize, + /// The original length of `vec` prior to draining. + old_len: usize, + /// The filter test predicate. + pred: F, + /// A flag that indicates a panic has occurred in the filter test prodicate. + /// This is used as a hint in the drop implementation to prevent consumption + /// of the remainder of the `DrainFilter`. Any unprocessed items will be + /// backshifted in the `vec`, but no further items will be dropped or + /// tested by the filter predicate. + panic_flag: bool, +} + +#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")] +impl<T, F> Iterator for DrainFilter<'_, T, F> +where + F: FnMut(&mut T) -> bool, +{ + type Item = T; + + fn next(&mut self) -> Option<T> { + unsafe { + while self.idx < self.old_len { + let i = self.idx; + let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len); + self.panic_flag = true; + let drained = (self.pred)(&mut v[i]); + self.panic_flag = false; + // Update the index *after* the predicate is called. If the index + // is updated prior and the predicate panics, the element at this + // index would be leaked. + self.idx += 1; + if drained { + self.del += 1; + return Some(ptr::read(&v[i])); + } else if self.del > 0 { + let del = self.del; + let src: *const T = &v[i]; + let dst: *mut T = &mut v[i - del]; + ptr::copy_nonoverlapping(src, dst, 1); + } + } + None + } + } + + fn size_hint(&self) -> (usize, Option<usize>) { + (0, Some(self.old_len - self.idx)) + } +} + +#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")] +impl<T, F> Drop for DrainFilter<'_, T, F> +where + F: FnMut(&mut T) -> bool, +{ + fn drop(&mut self) { + struct BackshiftOnDrop<'a, 'b, T, F> + where + F: FnMut(&mut T) -> bool, + { + drain: &'b mut DrainFilter<'a, T, F>, + } + + impl<'a, 'b, T, F> Drop for BackshiftOnDrop<'a, 'b, T, F> + where + F: FnMut(&mut T) -> bool, + { + fn drop(&mut self) { + unsafe { + if self.drain.idx < self.drain.old_len && self.drain.del > 0 { + // This is a pretty messed up state, and there isn't really an + // obviously right thing to do. We don't want to keep trying + // to execute `pred`, so we just backshift all the unprocessed + // elements and tell the vec that they still exist. The backshift + // is required to prevent a double-drop of the last successfully + // drained item prior to a panic in the predicate. + let ptr = self.drain.vec.as_mut_ptr(); + let src = ptr.add(self.drain.idx); + let dst = src.sub(self.drain.del); + let tail_len = self.drain.old_len - self.drain.idx; + src.copy_to(dst, tail_len); + } + self.drain.vec.set_len(self.drain.old_len - self.drain.del); + } + } + } + + let backshift = BackshiftOnDrop { drain: self }; + + // Attempt to consume any remaining elements if the filter predicate + // has not yet panicked. We'll backshift any remaining elements + // whether we've already panicked or if the consumption here panics. + if !backshift.drain.panic_flag { + backshift.drain.for_each(drop); + } + } +} |