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Thread-Topic: RFC: CachedIterable (rewindable, allows any key&repeating keys)
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Date: Wed, 9 Jun 2021 00:22:33 +0000
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Subject: Re: RFC: CachedIterable (rewindable, allows any key&repeating keys)
From: tysonandre775@hotmail.com (tyson andre)

Hi internals,=0A=
=0A=
> I've created a new RFC https://wiki.php.net/rfc/cachediterable adding Cac=
hedIterable,=0A=
> which eagerly evaluates any iterable and contains an immutable copy of th=
e keys and values of the iterable it was constructed from=0A=
> =0A=
> This has the proposed signature:=0A=
> =0A=
> ```=0A=
> final class CachedIterable implements IteratorAggregate, Countable, JsonS=
erializable=0A=
> {=0A=
> =A0=A0=A0 public function __construct(iterable $iterator) {}=0A=
> =A0=A0=A0 public function getIterator(): InternalIterator {}=0A=
> =A0=A0=A0 public function count(): int {}=0A=
> =A0=A0=A0 // [[$key1, $value1], [$key2, $value2]]=0A=
> =A0=A0=A0 public static function fromPairs(array $pairs): CachedIterable =
{}=0A=
> =A0=A0=A0 // [[$key1, $value1], [$key2, $value2]]=0A=
> =A0=A0=A0 public function toPairs(): array{} =0A=
> =A0=A0=A0 public function __serialize(): array {}=A0 // [$k1, $v1, $k2, $=
v2,...]=0A=
> =A0=A0=A0 public function __unserialize(array $data): void {}=0A=
> =A0=0A=
> =A0=A0=A0 // useful for converting iterables back to arrays for further p=
rocessing=0A=
> =A0=A0=A0 public function keys(): array {}=A0 // [$k1, $k2, ...]=0A=
> =A0=A0=A0 public function values(): array {}=A0 // [$v1, $v2, ...]=0A=
> =A0=A0=A0 // useful to efficiently get offsets at the middle/end of a lon=
g iterable=0A=
> =A0=A0=A0 public function keyAt(int $offset): mixed {}=0A=
> =A0=A0=A0 public function valueAt(int $offset): mixed {}=0A=
> =A0=0A=
> =A0=A0=A0 // '[["key1","value1"],["key2","value2"]]' instead of '{...}'=
=0A=
> =A0=A0=A0 public function jsonSerialize(): array {}=0A=
> =A0=A0=A0 // dynamic properties are forbidden=0A=
> }=0A=
> ```=0A=
> =0A=
> Currently, PHP does not provide a built-in way to store the state of an a=
rbitrary iterable for reuse later=0A=
> (when the iterable has arbitrary keys, or when keys might be repeated). I=
t would be useful to do so for many use cases, such as:=0A=
> =0A=
> 1. Creating a rewindable copy of a non-rewindable Traversable =0A=
> 2. Generating an IteratorAggregate from a class still implementing Iterat=
or=0A=
> 3. In the future, providing internal or userland helpers such as iterable=
_flip(iterable $input), iterable_take(iterable $input, int $limit),=0A=
> =A0=A0=A0 iterable_chunk(iterable $input, int $chunk_size), iterable_reve=
rse(), etc (these are not part of the RFC)=0A=
> 4. Providing memory-efficient random access to both keys and values of ar=
bitrary key-value sequences =0A=
> =0A=
> Having this implemented as an internal class would also allow it to be mu=
ch more efficient than a userland solution=0A=
> (in terms of time to create, time to iterate over the result, and total m=
emory usage). See https://wiki.php.net/rfc/cachediterable#benchmarks=0A=
> =0A=
> After some consideration, this is being created as a standalone RFC, and =
going in the global namespace:=0A=
> =0A=
> - Based on early feedback on https://wiki.php.net/rfc/any_all_on_iterable=
#straw_poll (on the namespace preferred in previous polls)=0A=
> =A0 It seems like it's way too early for me to be proposing namespaces in=
 any RFCs for PHP adding to modules that already exist, when there is no co=
nsensus.=0A=
> =0A=
> =A0 An earlier attempt by others on creating a policy for namespaces in g=
eneral(https://wiki.php.net/rfc/php_namespace_policy#vote) also did not pas=
s.=0A=
> =0A=
> =A0 Having even 40% of voters opposed to introducing a given namespace (i=
n pre-existing modules)=0A=
> =A0 makes it an impractical choice when RFCs require a 2/3 majority to pa=
ss.=0A=
> - While some may argue that a different namespace might pass,=0A=
> =A0 https://wiki.php.net/rfc/any_all_on_iterable_straw_poll_namespace#vot=
e had a sharp dropoff in feedback after the 3rd form.=0A=
> =A0 I don't know how to interpret that - e.g. are unranked namespaces pre=
ferred even less than the options that were ranked or just not seen as affe=
cting the final result.=0A=
=0A=
A heads up - I will probably start voting on https://wiki.php.net/rfc/cache=
diterable this weekend after https://wiki.php.net/rfc/cachediterable_straw_=
poll is finished.=0A=
=0A=
Any other feedback on CachedIterable?=0A=
=0A=
Thanks,=0A=
Tyson=0A=