drain.rs.html -- source
Description: Source to the Rust file `src\liballoc\collections\vec_deque\drain.rs`.
Keywords: rust, rustlang, rust-lang

      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126

    use core::iter::FusedIterator;
    use core::ptr::{self, NonNull};
    use core::{fmt, mem};

    use super::{count, Iter, 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`]: struct.VecDeque.html#method.drain
    /// [`VecDeque`]: struct.VecDeque.html
    #[stable(feature = "drain", since = "1.6.0")]
    pub struct Drain<'a, T: 'a> {
        pub(crate) after_tail: usize,
        pub(crate) after_head: usize,
        pub(crate) iter: Iter<'a, T>,
        pub(crate) deque: NonNull<VecDeque<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.after_tail)
                .field(&self.after_head)
                .field(&self.iter)
                .finish()
        }
    }

    #[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> Drop for Drain<'_, T> {
        fn drop(&mut self) {
            struct DropGuard<'r, 'a, T>(&'r mut Drain<'a, T>);

            impl<'r, 'a, T> Drop for DropGuard<'r, 'a, T> {
                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> Iterator for Drain<'_, T> {
        type Item = T;

        #[inline]
        fn next(&mut self) -> Option<T> {
            self.iter.next().map(|elt| unsafe { ptr::read(elt) })
        }

        #[inline]
        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) })
        }
    }

    #[stable(feature = "drain", since = "1.6.0")]
    impl<T> ExactSizeIterator for Drain<'_, T> {}

    #[stable(feature = "fused", since = "1.26.0")]
    impl<T> FusedIterator for Drain<'_, T> {}