Clarify Collections' interaction with Traversible<object, mixed>, such as WeakMap

[Vectorial1024]

Laravel Version

10.33

PHP Version

8.1.5

Database Driver & Version

N/A

Description

Laravel has collect() to produce a Collection; currently, the Collection accepts many types, one of which is PHP's Traversible.

It looks fine, but a problem: WeakMap implements Traversible. From the constructor definition/hinting, WeakMap instances are valid Collection "items". But as soon as such Collections are instantiated, a fatal error is always thrown:

TypeError: Illegal offset type.

Clearly, the underlying data structure of the Collection is an array, which obviously cannot accept objects as keys.

This is quite undocumented in the official Laravel docs in the Laravel website. However, the existing Collection constructor did not really check against WeakMaps.

I do know a bit about the covariance-contravariance thing that makes it a bit difficult to specifically reject WeakMap instances during typehinting.

A clarification is very much appreciated:

• If Collections should not accept WeakMap, then perhaps the docs should be updated with this info; or, a more specific error message could be printed.
• If Collections are supposed to accept WeakMap, then perhaps the Collection class needs some refactoring.

---

One very jarring experience with Laravel, is that e.g. I can do filter() on "real array" Collections, but I cannot do filter() on WeakMap instances, even when in native PHP, both can be traversed with something like

function filter(array|WeakMap $original, callable|Closure $predicate)
{
    $results = is_array($original) ? [] : new WeakMap();
    foreach ($original as $key => $value) {
        if ($predicate($value)) {
            $results[$key] = $value;
        }
    }
    return $results;
}

Steps To Reproduce

Using php artisan tinker [file]:

File contents:

<?php

$testMap = new WeakMap();
$testInstance = new stdClass();
$testInstance->haha = 'yes';
$testMap[$testInstance] = 3;

// should the following line be allowed or rejected?
$testCollection = collect($testMap);
// TypeError: Illegal offset type

// unreachable code: unhandled exception thrown
$testCollection->each(fn($x) => var_dump($x));

[crynobone]

Submitted a PR to throw exception when trying to use $testCollection = collect($testMap);

[Vectorial1024]

Slow down! The problem is not that trivial.

I did some more research after submitting this, and realized WeakMap is not the only class affected by this clarification. For example, SplObjectStorage is also affected by this, because it instanceof Traversible, but obviously its keys are all objects, and then it cannot be sent into a Collection.

Basically, any class that is Traversible is a potential incompatible class of Collection. To throw more accurate exceptions, we will need to check whether the keys of Traversible is of the pseudotype array-key (basically int|string).

We will never know how many such incompatible classes out there that extends Traversible but have their keys in object type.

Therefore, the question remains:

• refactor Collections to allow object keys?
• improve detection of Traversible<object, mixed>?

[Vectorial1024]

I noticed this flag in iterator_to_array:

• preserve_keys

Will setting it to false help with the situation? I see mentions of doing so to give out items inside SplObjectStorage instances.

[crynobone]

You can't convert WeakMap to an array and we not planning to add support for WeakMap using Collection at the moment.