tag	e89849673646d19fde8b9160f96af578962c93aa
tagger	The Android Open Source Project <initial-contribution@android.com>	Thu Feb 02 03:14:07 2023 -0800
object	fc80031f7e12e5d81d579011cd9de7ef6c49a278

commit	fc80031f7e12e5d81d579011cd9de7ef6c49a278	[log] [tgz]
author	Android Build Coastguard Worker <android-build-coastguard-worker@google.com>	Tue May 10 07:04:15 2022 +0000
committer	Android Build Coastguard Worker <android-build-coastguard-worker@google.com>	Tue May 10 07:04:15 2022 +0000
tree	3547624fc1bb0a71350ed06a100ae37654e76022
parent	b443866a111da5bb9023df17bde37cfc7e589af4 [diff]
parent	f52288a4b7cf8ce70ec0b7c9ce819bffcb18dcf7 [diff]

tree: 3547624fc1bb0a71350ed06a100ae37654e76022

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.

// 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));