Proposal: Adding a RewindableKeyValueIterator type allowing mixed/repeated keys

Hi internals, Currently, there don't seem to be any internal classes that can be used to store a copy of the keys and values of an arbitrary Traversable. - This would help in eagerly evaluating the result of a generator in a memory efficient way that could be exactly stored and reused e.g. return $this->cachedResults ??= new \RewindableKeyValueIterator($this->innerResultsGenerator()); https://externals.io/message/108767#108797 - This would be useful to exactly represent the keys of sequences with repeated keys (e.g. yield 'first'; yield 'second'; implicitly uses the key 0 twice.) - This would be convenient to have to differentiate between 1, '1', and true. - This would be useful if php were to add internal global functions that act on iterables and return Traversables with potentially repeated keys based on those iterables, e.g. map(), filter(), take(), flip(), etc - If PHP were to add more iterable methods, being able to save an immutable copy of a traversable's result would be useful for end users. - If PHP were to add a Map (ordered hash map with null/any scalar/arrays/objects as keys) class type in the future, and that implemented IteratorAggregate, the return type of getIterator() would need something like RewindableKeyValueIterator. - The lack of a relevant datatype is among the reasons why classes such as SplObjectStorage are still an Iterator instead of an IteratorAggregate. (and backwards compatibility) ``` final class KeyValueSequenceIterator implements Iterator { // loop over all values in $values and store a copy, converting // references in top-level array values to non-references public function __construct(iterable $values) {...} public static function fromKeyValuePairs(iterable $entries): self {...} // fromKeyValuePairs([[$key1, $value1]]) public function rewind(): void {...} public function next(): void {...} public function current(): mixed {...} public function key(): mixed {...} public function valid(): bool {...} // and __debugInfo, __clone(), etc. } ``` Thanks, - Tyson