PHP RFC: Iterator chaining

• Version: 0.9
• Date: 2021-03-20
• Author: Max Semenik, maxsem.wiki@gmail.com
• Status: Draft
• First Published at: http://wiki.php.net/rfc/iterator_chaining

SPL provides a set of iterators that allow feeding one into another to create powerful data pipelines, however doing that is not particularly convenient:

$iterator = new RegexIterator($myIterator, '/some pattern/');
$iterator = new CallbackFilterIterator($iterator, fn(...) {...});
$iterator = new LimitIterator($iterator, 0, 123);
$iterator = new InfiniteIterator($iterator);

Phew, that's a lot of typing! Not easy to comprehend, either. Alternatively, a functional approach could be used:

$iterator = new InfiniteIterator(new LimitIterator(new CallbackFilterIterator(new RegexIterator($myIterator, '/some pattern/'), fn(...) {...}), 0, 123));

Note how the order of writing is gorgeously opposite to the order of data flow.

Create a trait that extends iterators and allows to feed them into other iterators:

trait IteratorChain {
    public function skip(int $count): LimitIterator {}
    public function regexFilter(string $regex, int $mode = RegexIterator::MATCH, int $flags = 0 , int $preg_flags = 0): RegexIterator {}
    public function callbackFilter(callable $callback): CallbackIterator {}
    public function noRewind(): NoRewindIterator {}
    public function cached(int $flags = CachingIterator::CALL_TOSTRING): CachingIterator {}
    public function multiple(int $flags = MultipleIterator::MIT_NEED_ALL|MultipleIterator::MIT_KEYS_NUMERIC, string|int|null $info = null): MultipleIterator {}
    public function infinite(): InfiniteIterator {}
}

Use this trait in all SPL iterators, where appropriate. Full list:

• ArrayIterator
• DirectoryIterator
• EmptyIterator - for uniformness
• IteratorIterator and thus all its subclasses
• MultipleIterator
• RecursiveArrayIterator

What breaks, and what is the justification for it?

8.1.

Should not impact existing functionality (other than making some of it easier to use).

Need to

List existing areas/features of PHP that will not be changed by the RFC.

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