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use core::fmt;
use core::iter::FusedIterator;
use core::marker::PhantomData;
use core::mem::{self, MaybeUninit};
use core::ptr::{self, NonNull};
use crate::alloc::{Allocator, Global};
use super::{count, wrap_index, VecDeque};
/// A draining iterator over the elements of a `VecDeque`.
///
/// This `struct` is created by the [`drain`] method on [`VecDeque`]. See its
/// documentation for more.
///
/// [`drain`]: VecDeque::drain
#[stable(feature = "drain", since = "1.6.0")]
pub struct Drain<
'a,
T: 'a,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> {
after_tail: usize,
after_head: usize,
ring: NonNull<[T]>,
tail: usize,
head: usize,
deque: NonNull<VecDeque<T, A>>,
_phantom: PhantomData<&'a T>,
}
impl<'a, T, A: Allocator> Drain<'a, T, A> {
pub(super) unsafe fn new(
after_tail: usize,
after_head: usize,
ring: &'a [MaybeUninit<T>],
tail: usize,
head: usize,
deque: NonNull<VecDeque<T, A>>,
) -> Self {
let ring = unsafe { NonNull::new_unchecked(ring as *const [MaybeUninit<T>] as *mut _) };
Drain { after_tail, after_head, ring, tail, head, deque, _phantom: PhantomData }
}
}
#[stable(feature = "collection_debug", since = "1.17.0")]
impl<T: fmt::Debug, A: Allocator> fmt::Debug for Drain<'_, T, A> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("Drain")
.field(&self.after_tail)
.field(&self.after_head)
.field(&self.ring)
.field(&self.tail)
.field(&self.head)
.finish()
}
}
#[stable(feature = "drain", since = "1.6.0")]
unsafe impl<T: Sync, A: Allocator + Sync> Sync for Drain<'_, T, A> {}
#[stable(feature = "drain", since = "1.6.0")]
unsafe impl<T: Send, A: Allocator + Send> Send for Drain<'_, T, A> {}
#[stable(feature = "drain", since = "1.6.0")]
impl<T, A: Allocator> Drop for Drain<'_, T, A> {
fn drop(&mut self) {
struct DropGuard<'r, 'a, T, A: Allocator>(&'r mut Drain<'a, T, A>);
impl<'r, 'a, T, A: Allocator> Drop for DropGuard<'r, 'a, T, A> {
fn drop(&mut self) {
self.0.for_each(drop);
let source_deque = unsafe { self.0.deque.as_mut() };
// T = source_deque_tail; H = source_deque_head; t = drain_tail; h = drain_head
//
// T t h H
// [. . . o o x x o o . . .]
//
let orig_tail = source_deque.tail;
let drain_tail = source_deque.head;
let drain_head = self.0.after_tail;
let orig_head = self.0.after_head;
let tail_len = count(orig_tail, drain_tail, source_deque.cap());
let head_len = count(drain_head, orig_head, source_deque.cap());
// Restore the original head value
source_deque.head = orig_head;
match (tail_len, head_len) {
(0, 0) => {
source_deque.head = 0;
source_deque.tail = 0;
}
(0, _) => {
source_deque.tail = drain_head;
}
(_, 0) => {
source_deque.head = drain_tail;
}
_ => unsafe {
if tail_len <= head_len {
source_deque.tail = source_deque.wrap_sub(drain_head, tail_len);
source_deque.wrap_copy(source_deque.tail, orig_tail, tail_len);
} else {
source_deque.head = source_deque.wrap_add(drain_tail, head_len);
source_deque.wrap_copy(drain_tail, drain_head, head_len);
}
},
}
}
}
while let Some(item) = self.next() {
let guard = DropGuard(self);
drop(item);
mem::forget(guard);
}
DropGuard(self);
}
}
#[stable(feature = "drain", since = "1.6.0")]
impl<T, A: Allocator> Iterator for Drain<'_, T, A> {
type Item = T;
#[inline]
fn next(&mut self) -> Option<T> {
if self.tail == self.head {
return None;
}
let tail = self.tail;
self.tail = wrap_index(self.tail.wrapping_add(1), self.ring.len());
// Safety:
// - `self.tail` in a ring buffer is always a valid index.
// - `self.head` and `self.tail` equality is checked above.
unsafe { Some(ptr::read(self.ring.as_ptr().get_unchecked_mut(tail))) }
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let len = count(self.tail, self.head, self.ring.len());
(len, Some(len))
}
}
#[stable(feature = "drain", since = "1.6.0")]
impl<T, A: Allocator> DoubleEndedIterator for Drain<'_, T, A> {
#[inline]
fn next_back(&mut self) -> Option<T> {
if self.tail == self.head {
return None;
}
self.head = wrap_index(self.head.wrapping_sub(1), self.ring.len());
// Safety:
// - `self.head` in a ring buffer is always a valid index.
// - `self.head` and `self.tail` equality is checked above.
unsafe { Some(ptr::read(self.ring.as_ptr().get_unchecked_mut(self.head))) }
}
}
#[stable(feature = "drain", since = "1.6.0")]
impl<T, A: Allocator> ExactSizeIterator for Drain<'_, T, A> {}
#[stable(feature = "fused", since = "1.26.0")]
impl<T, A: Allocator> FusedIterator for Drain<'_, T, A> {}
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