commit	0c4e551e3d27445adb895b4e7f7b65752e12a815	[log] [tgz]
author	Chih-Hung Hsieh <chh@google.com>	Mon Oct 12 10:52:42 2020 +0000
committer	Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>	Mon Oct 12 10:52:42 2020 +0000
tree	4e40e09e8393fb852da23eb4920b16e47d782a7e
parent	42867bc476f708c5b2e76d4ef96faa74eaad3847 [diff]
parent	cf9c2bd7266ab557d639c85ec7b1b02da0130409 [diff]

tree: 4e40e09e8393fb852da23eb4920b16e47d782a7e

README.md

`peeking_take_while`

Provides the peeking_take_while iterator adaptor method.

The peeking_take_while method is very similar to take_while, but behaves differently when used with a borrowed iterator (perhaps returned by Iterator::by_ref).

peeking_take_while peeks at the next item in the iterator and runs the predicate on that peeked item. This avoids consuming the first item yielded by the underlying iterator for which the predicate returns false. On the other hand, take_while will consume that first item for which the predicate returns false, and it will be lost.

extern crate peeking_take_while;

// Bring the `peeking_take_while` method for peekable iterators into
// scope.
use peeking_take_while::PeekableExt;

// Let's say we have two collections we want to iterate through: `xs` and
// `ys`. We want to perform one operation on all the leading contiguous
// elements that match some predicate, and a different thing with the rest of
// the elements. With the `xs`, we will use the normal `take_while`. With the
// `ys`, we will use `peeking_take_while`.

let xs: Vec<u8> = (0..100).collect();
let ys = xs.clone();

let mut iter_xs = xs.into_iter();
let mut iter_ys = ys.into_iter().peekable();

{
    // Let's do one thing with all the items that are less than 10.

    let xs_less_than_ten = iter_xs.by_ref().take_while(|x| *x < 10);
    for x in xs_less_than_ten {
        do_things_with(x);
    }

    let ys_less_than_ten = iter_ys.by_ref().peeking_take_while(|y| *y < 10);
    for y in ys_less_than_ten {
        do_things_with(y);
    }
}

// And now we will do some other thing with the items that are greater than
// or equal to 10.

// ...except, when using plain old `take_while` we lost 10!
assert_eq!(iter_xs.next(), Some(11));

// However, when using `peeking_take_while` we did not! Great!
assert_eq!(iter_ys.next(), Some(10));