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Implementation for rust-lang/libs-team#138 #105072

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Implementation for rust-lang/libs-team#138 #105072

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19e6695
fix typo in comment
Sp00ph Nov 29, 2022
327b94a
Make `VecDeque::{new,new_in}` `const fn`s
Sp00ph Nov 29, 2022
a06f7f8
Add O(1) `Vec -> VecDeque` conversion guarantee
Sp00ph Nov 29, 2022
82fc730
Use `CURRENT_RUSTC_VERSION` placeholder
Sp00ph Nov 29, 2022
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18 changes: 9 additions & 9 deletions library/alloc/src/collections/vec_deque/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -531,12 +531,13 @@ impl<T> VecDeque<T> {
///
/// let deque: VecDeque<u32> = VecDeque::new();
/// ```
// FIXME: This should probably be const
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_vec_deque_new", since = "CURRENT_RUSTC_VERSION")]
#[must_use]
pub fn new() -> VecDeque<T> {
VecDeque::new_in(Global)
pub const fn new() -> VecDeque<T> {
// FIXME: This should just be `VecDeque::new_in(Global)` once that's stable.
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You could also slap #[allow_internal_unstable(allocator_api)] onto VecDeque::new instead. Not sure if that's frowned upon though. What does the library team say?

VecDeque { head: 0, len: 0, buf: RawVec::NEW }
}

/// Creates an empty deque with space for at least `capacity` elements.
Expand Down Expand Up @@ -566,10 +567,9 @@ impl<T, A: Allocator> VecDeque<T, A> {
///
/// let deque: VecDeque<u32> = VecDeque::new();
/// ```
// FIXME: This should probably be const
#[inline]
#[unstable(feature = "allocator_api", issue = "32838")]
pub fn new_in(alloc: A) -> VecDeque<T, A> {
pub const fn new_in(alloc: A) -> VecDeque<T, A> {
VecDeque { head: 0, len: 0, buf: RawVec::new_in(alloc) }
}

Expand Down Expand Up @@ -2152,7 +2152,7 @@ impl<T, A: Allocator> VecDeque<T, A> {

self.head = tail;
} else {
// ´free` is smaller than both `head_len` and `tail_len`.
// `free` is smaller than both `head_len` and `tail_len`.
// the general algorithm for this first moves the slices
// right next to each other and then uses `slice::rotate`
// to rotate them into place:
Expand Down Expand Up @@ -2789,9 +2789,9 @@ impl<T, A: Allocator> From<Vec<T, A>> for VecDeque<T, A> {
/// [`Vec<T>`]: crate::vec::Vec
/// [`VecDeque<T>`]: crate::collections::VecDeque
///
/// In its current implementation, this is a very cheap
/// conversion. This isn't yet a guarantee though, and
/// shouldn't be relied on.
/// This conversion is guaranteed to run in *O*(1) time
/// and to not re-allocate the `Vec`'s buffer or
/// allocate any additional memory.
fn from(other: Vec<T, A>) -> Self {
let (ptr, len, cap, alloc) = other.into_raw_parts_with_alloc();
Self { head: 0, len, buf: unsafe { RawVec::from_raw_parts_in(ptr, cap, alloc) } }
Expand Down