Add Iterator::at_least() and Iterator::at_most() API

[Folyd]

at_least() and at_most() are similar to any() and all(), these two methods test if at least/most n elements of the iterator matches a predicate.

Although, we can simply use iter.filter().count() > n , at_least() and at_most() are short-circuiting, so it's more effecency than the simple filter in most cases.

I have created a benchmark project to demonstrate three versions of at_least, here is the repository link.

[rust-highfive]

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[the8472]

Although, we can simply use iter.filter().count() > n , at_least() and at_most() are short-circuiting, so it's more effecency than the simple filter in most cases.

Well, that effect could also be achieved by adding a take(n) before the count().

[bors]

☔ The latest upstream changes (presumably #81089) made this pull request unmergeable. Please resolve the merge conflicts.

[Folyd]

@the8472 TIL. Good point. Thanks. 😄

So I'm wondering why the implementation of Iterator::any() is based on ControlFlow ranther than something like filter(|f| f()).take(1).count() > 0?

[bors]

☔ The latest upstream changes (presumably #82953) made this pull request unmergeable. Please resolve the merge conflicts.

[crlf0710]

r? @m-ou-se

[crlf0710]

Triage: There's merge conflicts now. @Folyd

[m-ou-se]

@Folyd Thanks for your PR!

Do you have some motivating examples? While .any() and .all() seem like very common operations to me, I can't think of many common situations where .at_least() and .at_most() would be used. Considering the very large amount of methods we already have on Iterator and that .filter().take() already suffices in most (all?) of those situations, I'm hesitant to merge this.

[Folyd]

@Folyd Thanks for your PR!

Do you have some motivating examples? While .any() and .all() seem like very common operations to me, I can't think of many common situations where .at_least() and .at_most() would be used. Considering the very large amount of methods we already have on Iterator and that .filter().take() already suffices in most (all?) of those situations, I'm hesitant to merge this.

Thanks, @m-ou-se. I agree with you. Let's close this. 👌