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Organization: Aimeos GmbH
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Date: Tue, 19 Nov 2019 23:21:26 +0100
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Subject: [RFC] "arrayable" pseudo type hint
From: norbert@aimeos.com (Aimeos | Norbert Sendetzky)

Since PHP 7.1, there's the "iterable" pseudo type hint that matches
"array" or "Traversable".

PHP frameworks would profit from support of an "arrayable" pseudo type
hint that matches "array" and all objects that can be used like arrays.

For that, "arrayable" objects have to implement these interfaces:
- ArrayAccess
- Countable
- Traversable (i.e. either Iterator or IteratorAggregate)


Implementing "arrayable" pseudo type, we could pass arrays or all
objects that can be used like arrays to methods and do:

function useArrayable( arrayable $arg ) : arrayable {
    $cnt = count( $arg );
    $value = $arg['key'];
    foreach( $arg as $key => $entry );
    return $arg;
}


Best use cases are:

- Laravel Collection
(https://github.com/laravel/framework/blob/6.x/src/Illuminate/Support/Collection.php)

- Aimeos Map (https://github.com/aimeos/map)


No new interface is proposed because we can check if objects implement:

ArrayAccess && Countable && Traversable


Because "array" !== "arrayable", "arrayable objects will not be accepted
by array_* functions and all functions that only use "array" as type
hint for parameters and return types.


This proposal is not obsolete by the implementation of union types (i.e.
array|Traversable) because union data types are types/interfaces
combined by OR. "arrayable" is a combination of OR and AND:

array|ArrayAccess&Countable&Traversable


Also, "arrayable" won't supersede "iterable" because

- "iterable" matches arrays, iterators and generators

- "arrayable" matches arrays and objects that can be used like arrays


"Can be used like arrays" doesn't include support for empty() because it
works for empty arrays but not for "arrayable" objects without elements.
If possible and requested, this may be addressed by another RFC.


As Larry Garfield suggested, this pre-RFC proposes concentrates on the
"arrayable" pseudo type only.

It does NOT discusses that:

- arrayable objects can be converted to arrays (Steven Wade works on an
RFC for a __toArray() magic function)

- ArrayObject or any other arrayable object makes the array_* functions
less relevant in the future

- arrayable objects can be passed to array_* functions in the future