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Add Iterator::exhaust #49990

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Add Iterator::exhaust #49990

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907e405
Correct typo in Iterator::product
varkor Apr 15, 2018
804532c
Add Iterator::exhaust
varkor Apr 15, 2018
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Add Iterator::exhaust
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@varkor
varkor committed Apr 15, 2018
commit 804532c9fd8df68e71fc491148fef512ac0d301f
26 changes: 26 additions & 0 deletions src/libcore/iter/iterator.rs
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Expand Up @@ -2251,6 +2251,32 @@ pub trait Iterator {
Product::product(self)
}

/// Eagerly consume the iterator, evaluating all the elements.
///
/// This is primarily useful for evaluating the effects of an iterator that
/// has previously been created. To evaluate the effects of an iterator
/// immediately, it is likely better to use [`for_each`].
///
/// [`for_each`]: #method.for_each
///
/// # Examples
///
/// ```
/// // Prepare an iterator with side effects...
/// let count_aloud = 1..=10.map(|x| println!("{}", x));
///
/// // ...
///
/// // Trigger the effects!
/// count_aloud.exhaust();
///
/// ```
#[inline]
#[unstable(feature = "iter_exhaust", issue = "44546")]
fn exhaust(self) where Self: Sized {
for _ in self {}
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This should use for_each to get internal iteration, rather than (implicit) next() calls.

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@varkor varkor Apr 16, 2018 •
edited
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It doesn't matter so much now the PR's closed, but out of curiosity, what difference in behaviour would using for_each have?

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The difference is that some iterators can apply a fold much more efficiently than they can next one item at a time. For instance, Chain::fold can fold its first part as a whole, then its second part as a whole, but Chain::next has to check whether it's on the first or second part every time. This is demonstrated in the benchmarks added to the for_each PR, #42782, in commit 4a8ddac.

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Ah, of course, that makes a lot of sense. Thanks for explaining!

}

/// Lexicographically compares the elements of this `Iterator` with those
/// of another.
#[stable(feature = "iter_order", since = "1.5.0")]
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