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core: Implement rfold for Map, Cloned, Chain

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This commit is contained in:
Ulrik Sverdrup 2017-09-18 21:27:19 +02:00
parent 31cf26a953
commit a59a25d8e6
1 changed files with 33 additions and 0 deletions
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33
src/libcore/iter/mod.rs
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@ -461,6 +461,12 @@ impl<'a, I, T: 'a> DoubleEndedIterator for Cloned<I>
fn next_back(&mut self) -> Option<T> {
self.it.next_back().cloned()
}
fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
where F: FnMut(Acc, Self::Item) -> Acc,
{
self.it.rfold(init, move |acc, elt| f(acc, elt.clone()))
}
}
#[stable(feature = "iter_cloned", since = "1.1.0")]
@ -773,6 +779,26 @@ impl<A, B> DoubleEndedIterator for Chain<A, B> where
ChainState::Back => self.b.next_back(),
}
}
fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
where F: FnMut(Acc, Self::Item) -> Acc,
{
let mut accum = init;
match self.state {
ChainState::Both | ChainState::Back => {
accum = self.b.rfold(accum, &mut f);
}
_ => { }
}
match self.state {
ChainState::Both | ChainState::Front => {
accum = self.a.rfold(accum, &mut f);
}
_ => { }
}
accum
}
}
// Note: *both* must be fused to handle double-ended iterators.
@ -1106,6 +1132,13 @@ impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F> where
fn next_back(&mut self) -> Option<B> {
self.iter.next_back().map(&mut self.f)
}
fn rfold<Acc, G>(self, init: Acc, mut g: G) -> Acc
where G: FnMut(Acc, Self::Item) -> Acc,
{
let mut f = self.f;
self.iter.rfold(init, move |acc, elt| g(acc, f(elt)))
}
}
#[stable(feature = "rust1", since = "1.0.0")]