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Thread-Topic: Proposal: Adding a RewindableKeyValueIterator type allowing
 mixed/repeated keys
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Date: Tue, 2 Feb 2021 14:59:25 +0000
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Subject: Re: Proposal: Adding a RewindableKeyValueIterator type allowing
 mixed/repeated keys
From: tysonandre775@hotmail.com (tyson andre)

Hi internals,=0A=
=0A=
> Currently, there don't seem to be any internal classes that can be used t=
o store a copy of the keys and values of an arbitrary Traversable.=0A=
> =0A=
> -=A0This would help in eagerly evaluating the result of a generator in a =
memory efficient way that could be exactly stored and reused =0A=
> =A0 e.g. `return $this->cachedResults ??=3D new \RewindableKeyValueIterat=
or($this->innerResultsGenerator());`=0A=
> =A0 https://externals.io/message/108767#108797=0A=
> - This would be useful to exactly represent the keys of sequences with re=
peated keys (e.g. `yield 'first'; yield 'second';` implicitly uses the key =
`0` twice.)=0A=
> - This would be convenient to have to differentiate between 1, '1', and t=
rue.=0A=
> - This would be useful if php were to add internal global functions that =
act on iterables and return Traversables with potentially repeated keys bas=
ed on those iterables,=0A=
> =A0=A0 e.g. map(), filter(), take(), flip(), etc=0A=
> - If PHP were to add more iterable methods, being able to save an immutab=
le copy of a traversable's result would be useful for end users.=0A=
> - If PHP were to add a Map (ordered hash map with null/any scalar/arrays/=
objects as keys) class type in the future,=0A=
> =A0 and that implemented IteratorAggregate, the return type of getIterato=
r() would need something like RewindableKeyValueIterator.=0A=
> - The lack of a relevant datatype is among the reasons why classes such a=
s SplObjectStorage are still an Iterator instead of an IteratorAggregate. (=
and backwards compatibility)=0A=
> =0A=
> ```=0A=
> final class KeyValueSequenceIterator implements Iterator {=0A=
> =A0=A0=A0 // loop over all values in $values and store a copy, converting=
=0A=
> =A0=A0=A0 // references in top-level array values to non-references=0A=
> =A0=A0=A0 public function __construct(iterable $values) {...}=0A=
> =A0=A0=A0 public static function fromKeyValuePairs(iterable $entries): se=
lf {...} // fromKeyValuePairs([[$key1, $value1]])=0A=
> =A0=A0=A0 public function rewind(): void {...}=0A=
> =A0=A0=A0 public function next(): void {...}=0A=
> =A0=A0=A0 public function current(): mixed {...}=0A=
> =A0=A0=A0 public function key(): mixed {...}=0A=
> =A0=A0=A0 public function valid(): bool {...}=0A=
> =A0=A0=A0 // and __debugInfo, __clone(), etc.=0A=
> }=0A=
> ```=0A=
=0A=
This has been updated - the preferred name is CachedIterable.=0A=
It turns out InternalIterator is generally more efficient, =0A=
and SplFixedArray is already using that.=0A=
The implementation is pretty much done - https://github.com/php/php-src/pul=
l/6655=0A=
=0A=
```=0A=
/**=0A=
 * Internal class that can be used to eagerly evaluate and store a copy=0A=
 * of the keys and values of an arbitrary Traversable.=0A=
 * Keys can be any type, and keys can be repeated.=0A=
 */=0A=
final class CachedIterable implements IteratorAggregate, Countable=0A=
{=0A=
    public function __construct(iterable $iterator) {}=0A=
    public function getIterator(): InternalIterator {}=0A=
    public function count(): int {}=0A=
    public static function fromPairs(array $pairs): CachedIterable;=0A=
=0A=
    public function __serialize(): array {}  // [$k1, $v1, $k2, $v2,...]=0A=
    public function __unserialize(array $data): void {}=0A=
=0A=
    // useful for converting iterables back to values=0A=
    public function keys(): array {}=0A=
    public function values(): array {}=0A=
    // useful to efficiently get offsets at the middle/end of a long iterab=
le.=0A=
    public function keyAt(int $offset): mixed {}=0A=
    public function valueAt(int $offset): mixed {}=0A=
    // dynamic properties are forbidden=0A=
}=0A=
```=0A=
=0A=
Any other comments?=0A=
=0A=
Thanks,=0A=
- Tyson=0A=