Bug: 154051565

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  1. 71d8216 Update TEST_MAPPING by Jeff Vander Stoep · 10 days ago master
  2. 73623b5 Merge "Update TEST_MAPPING" am: b64d2b1a58 am: e0b6b4b058 am: 7c6cfb021b am: 9c0effdcb0 by Treehugger Robot · 8 months ago main-16k-with-phones
  3. 9c0effd Merge "Update TEST_MAPPING" am: b64d2b1a58 am: e0b6b4b058 am: 7c6cfb021b by Treehugger Robot · 8 months ago
  4. 7c6cfb0 Merge "Update TEST_MAPPING" am: b64d2b1a58 am: e0b6b4b058 by Treehugger Robot · 8 months ago main-16k
  5. e0b6b4b Merge "Update TEST_MAPPING" am: b64d2b1a58 by Treehugger Robot · 8 months ago

peeking_take_while

Build Status

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));