library/core/src/iter/adapters/by_ref_sized.rs

   1 use crate::ops::Try;
   2
   3 /// Like `Iterator::by_ref`, but requiring `Sized` so it can forward generics.
   4 ///
   5 /// Ideally this will no longer be required, eventually, but as can be seen in
   6 /// the benchmarks (as of Feb 2022 at least) `by_ref` can have performance cost.
   7 pub(crate) struct ByRefSized<'a, I>(pub &'a mut I);
   8
   9 impl<I: Iterator> Iterator for ByRefSized<'_, I> {
  10     type Item = I::Item;
  11
  12     fn next(&mut self) -> Option<Self::Item> {
  13         self.0.next()
  14     }
  15
  16     fn size_hint(&self) -> (usize, Option<usize>) {
  17         self.0.size_hint()
  18     }
  19
  20     fn advance_by(&mut self, n: usize) -> Result<(), usize> {
  21         self.0.advance_by(n)
  22     }
  23
  24     fn nth(&mut self, n: usize) -> Option<Self::Item> {
  25         self.0.nth(n)
  26     }
  27
  28     fn fold<B, F>(self, init: B, f: F) -> B
  29     where
  30         F: FnMut(B, Self::Item) -> B,
  31     {
  32         self.0.fold(init, f)
  33     }
  34
  35     fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
  36     where
  37         F: FnMut(B, Self::Item) -> R,
  38         R: Try<Output = B>,
  39     {
  40         self.0.try_fold(init, f)
  41     }
  42 }