library/alloc/src/collections/vec_deque/pair_slices.rs

   1 use core::array;
   2 use core::cmp::{self};
   3 use core::mem::replace;
   4
   5 use super::VecDeque;
   6
   7 /// PairSlices pairs up equal length slice parts of two deques
   8 ///
   9 /// For example, given deques "A" and "B" with the following division into slices:
  10 ///
  11 /// A: [0 1 2] [3 4 5]
  12 /// B: [a b] [c d e]
  13 ///
  14 /// It produces the following sequence of matching slices:
  15 ///
  16 /// ([0 1], [a b])
  17 /// (\[2\], \[c\])
  18 /// ([3 4], [d e])
  19 ///
  20 /// and the uneven remainder of either A or B is skipped.
  21 pub struct PairSlices<'a, 'b, T> {
  22     pub(crate) a0: &'a mut [T],
  23     pub(crate) a1: &'a mut [T],
  24     pub(crate) b0: &'b [T],
  25     pub(crate) b1: &'b [T],
  26 }
  27
  28 impl<'a, 'b, T> PairSlices<'a, 'b, T> {
  29     pub fn from(to: &'a mut VecDeque<T>, from: &'b VecDeque<T>) -> Self {
  30         let (a0, a1) = to.as_mut_slices();
  31         let (b0, b1) = from.as_slices();
  32         PairSlices { a0, a1, b0, b1 }
  33     }
  34
  35     pub fn has_remainder(&self) -> bool {
  36         !self.b0.is_empty()
  37     }
  38
  39     pub fn remainder(self) -> impl Iterator<Item = &'b [T]> {
  40         array::IntoIter::new([self.b0, self.b1])
  41     }
  42 }
  43
  44 impl<'a, 'b, T> Iterator for PairSlices<'a, 'b, T> {
  45     type Item = (&'a mut [T], &'b [T]);
  46     fn next(&mut self) -> Option<Self::Item> {
  47         // Get next part length
  48         let part = cmp::min(self.a0.len(), self.b0.len());
  49         if part == 0 {
  50             return None;
  51         }
  52         let (p0, p1) = replace(&mut self.a0, &mut []).split_at_mut(part);
  53         let (q0, q1) = self.b0.split_at(part);
  54
  55         // Move a1 into a0, if it's empty (and b1, b0 the same way).
  56         self.a0 = p1;
  57         self.b0 = q1;
  58         if self.a0.is_empty() {
  59             self.a0 = replace(&mut self.a1, &mut []);
  60         }
  61         if self.b0.is_empty() {
  62             self.b0 = replace(&mut self.b1, &[]);
  63         }
  64         Some((p0, q0))
  65     }
  66 }