commit	ea4e336cbe0590017ab772ddb8db807f891fa48e	[log] [tgz]
author	Android Build Coastguard Worker <android-build-coastguard-worker@google.com>	Fri Nov 10 00:12:38 2023 +0000
committer	Android Build Coastguard Worker <android-build-coastguard-worker@google.com>	Fri Nov 10 00:12:38 2023 +0000
tree	f1a8519817402c05b61f50eed409dc10d105dc9a
parent	6a89a5f0abd88f8defc6325602b8fc293c9f8aff [diff]
parent	aceb1f0ab2efac4d4b76f36914c007cd7137b0f9 [diff]

tree: f1a8519817402c05b61f50eed409dc10d105dc9a

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));