Feature

The aim of this code is to be able to provide a closure to the $map parameter of the AsCollection::of() and AsCollection::using() methods, in order to be able to fully customize the creation of each item inside the collection.

public function casts(): array
{
    return [
        'collection' => AsCollection::of(function ($item) {
            // Custom logic here
        },
    ];
}

As casts needs to be serializable, I used the SerializableClosure in case a closure is used for the $map parameter.

I also extends this feature to the AsEncryptedCollection class:

public function casts(): array
{
    return [
        'collection' => AsEncryptedCollection::of(function ($item) {
            // Custom logic here
        },
    ];
}

Context

I want to use this new $map parameter (from the recent PR #55383) to generate a collection of data objects created with spatie/laravel-data, that are very well-suited for Eloquent casting. This is what I tried:

public function casts(): array
{
    return [
        'collection' => AsCollection::of([DataObject::class, 'from']),
    ];
}

To instantiate the data objects with the from() method, the Collection::map() method is used, which calls array_map([DataObject::class, 'from'], $array, $keys) internally. However, as the $keys are passed, the from() method thinks that these are properties of the DataObject, which is not.

With a closure, I would be able to do that to makes spatie/laravel-data objects works:

public function casts(): array
{
    return [
        'collection' => AsCollection::of(fn ($item) => DataObject::from($item)),
    ];
}