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Iterator Trait Parity
Aaron Rice edited this page Jul 28, 2025
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15 revisions
Here is a copy of the current Iterator trait along with some annotations on each of its methods.
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fn size_hint(&self) -> (usize, Option<usize>) { ... }- N/A, although in issue #146, I mentioned that it would be useful to be able to dynamically test if this is an exact vs bounded iterator; and in general it'd be great to be able to dynamically test even more than that --nmatsakis
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fn count(self) -> usize { ... } -
fn last(self) -> Option<Self::Item> { ... } -
fn nth(&mut self, n: usize) -> Option<Self::Item> { ... } -
fn step_by(self, step: usize) -> StepBy<Self> { ... } -
fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where U: IntoIterator<Item=Self::Item> { ... } -
fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where U: IntoIterator { ... } -
fn map<B, F>(self, f: F) -> Map<Self, F> where F: FnMut(Self::Item) -> B { ... } -
fn for_each<F>(self, f: F) where F: FnMut(Self::Item) -> () { ... } -
fn filter<P>(self, predicate: P) -> Filter<Self, P> where P: FnMut(&Self::Item) -> bool { ... } -
fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where F: FnMut(Self::Item) -> Option<B> { ... } -
fn enumerate(self) -> Enumerate<Self> { ... } -
fn peekable(self) -> Peekable<Self> { ... }- Inherently sequential --nmatsakis
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fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where P: FnMut(&Self::Item) -> bool { ... }- Inherently sequential --nmatsakis
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fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where P: FnMut(&Self::Item) -> bool { ... }- Inherently sequential --nmatsakis
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fn skip(self, n: usize) -> Skip<Self> { ... } -
fn take(self, n: usize) -> Take<Self> { ... } -
fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where F: FnMut(&mut St, Self::Item) -> Option<B> { ... }- https://github.com/rayon-rs/rayon/issues/329
- this is generally possible (it will be a bit different; more like
reduce), but it is non-trivial - it requires >1 pass and hence produces an intermediate collection
- basically you would do a parallel fold operation, performing a sequential scan for each segment
- the result of your scan is a
VecTree<Vec<T>>of same total length as your input iterator - this gives you partial sums (to consider one concrete application) at each point
- the result of your scan is a
- you can then traverse the tree (sequentially) to compute, for each vector, the total sum of preceding vectors
- you can then re-traverse the tree (in parallel) and add this total sum to each element of the vector (in place)
- that last step can itself drive another consumer, so this can still be a parallel adapter
- if we are clever, it can even be an exact one, though it will require a nice
VecTreeimplementation
- if we are clever, it can even be an exact one, though it will require a nice
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fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where F: FnMut(Self::Item) -> U, U: IntoIterator { ... } -
fn fuse(self) -> Fuse<Self> { ... }- Meh. I'm not sure how relevant this this. -- nmatsakis
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fn inspect<F>(self, f: F) -> Inspect<Self, F> where F: FnMut(&Self::Item) -> () { ... } -
fn by_ref(&mut self) -> &mut Self { ... }- Meh. Harder for us to support since we rely on taking ownership a lot to make ownership and safety work out, iirc.
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fn collect<B>(self) -> B where B: FromIterator<Self::Item> { ... } -
fn partition<B, F>(self, f: F) -> (B, B) where B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool { ... }- I've always thought this signature was wrong. Trying to remember why. =)
- At minimum, it should permit two distinct kinds of collections.
Still, it's interesting that the current FromParallelIterator can't support this.- https://github.com/rayon-rs/rayon/pull/326
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fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R where F: FnMut(B, Self::Item) -> R, R: Try<Ok = B> { ... } -
fn fold<B, F>(self, init: B, f: F) -> B where F: FnMut(B, Self::Item) -> B { ... } -
fn all<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool { ... } -
fn any<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool { ... } -
fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where P: FnMut(&Self::Item) -> bool { ... } -
fn position<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool { ... } -
fn rposition<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool, Self: ExactSizeIterator + DoubleEndedIterator { ... } -
fn max(self) -> Option<Self::Item> where Self::Item: Ord { ... } -
fn min(self) -> Option<Self::Item> where Self::Item: Ord { ... } -
fn max_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B { ... } -
fn max_by<F>(self, compare: F) -> Option<Self::Item> where F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... } -
fn min_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B { ... } -
fn min_by<F>(self, compare: F) -> Option<Self::Item> where F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... } -
fn rev(self) -> Rev<Self> where Self: DoubleEndedIterator { ... } -
fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Iterator<Item=(A, B)> { ... }- like partition, a bit tricky perhaps
- https://github.com/rayon-rs/rayon/pull/326
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fn cloned<'a, T>(self) -> Cloned<Self> where Self: Iterator<Item=&'a T>, T: 'a + Clone { ... } -
fn cycle(self) -> Cycle<Self> where Self: Clone { ... }- https://github.com/rayon-rs/rayon/issues/330
- This can probably be done for indexed parallel iterator, at least, sort of like chain?
- Have to think about it =)
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fn sum<S>(self) -> S where S: Sum<Self::Item> { ... } -
fn product<P>(self) -> P where P: Product<Self::Item> { ... } -
fn cmp<I>(self, other: I) -> Ordering where I: IntoIterator<Item=Self::Item>, Self::Item: Ord { ... } -
fn partial_cmp<I>(self, other: I) -> Option<Ordering> where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... } -
fn eq<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item> { ... } -
fn ne<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item> { ... } -
fn lt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... } -
fn le<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... } -
fn gt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... } -
fn ge<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }