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Don't call size_hint of underlying iterator needlessly

This commit is contained in:
Shotaro Yamada 2018-12-08 20:16:36 +09:00
parent e704ce9e8a
commit 5728a043e8
1 changed files with 10 additions and 2 deletions
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12
src/libcore/iter/mod.rs
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@ -2109,8 +2109,12 @@ impl<I: Iterator, P> Iterator for TakeWhile<I, P>
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
if self.flag {
(0, Some(0))
} else {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
}
#[inline]
@ -2321,6 +2325,10 @@ impl<I> Iterator for Take<I> where I: Iterator{
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
if self.n == 0 {
return (0, Some(0));
}
let (lower, upper) = self.iter.size_hint();
let lower = cmp::min(lower, self.n);