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To: Alex Bowers <bowersbros@gmail.com>, PHP <internals@lists.php.net>
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Date: Fri, 2 Dec 2016 15:04:30 +0100
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Subject: Re: [PHP-DEV] [Concept] Magic Casting
From: ivan.enderlin@hoa-project.net (Ivan Enderlin)

Hello :-),

Casting is already a very large surface of unsafety and bugs. Adding 
“magic” before this is like multiplying the surface by infinite.

The only goal I see here is to save a `new Collection(…)`, and this is 
not a sufficient reason from my point of view. If `array` was a type, 
and `IntoCollection` a trait, implemented for the `array` type, then we 
could do things like `[1, 2, 3].intoCollection()` for instance. However 
PHP does not bring this kind of features. So let's reverse this: 
`Collection::fromArray([1, 2, 3])`. But wait, this is exactly what `new 
Collection([1, 2, 3])` does for this specific case.

Do you have better use cases? A casting comes with a non-negligeable 
cost. You have to define your data clearly, and avoid casting as much as 
possible.

Cheers.


On 02.12.16 14:37, Alex Bowers wrote:
> Hello All,
>
> In PHP we currently have the ability to type hint classes in method
> signatures, however, sometimes it would be useful to convert the items to a
> different instance / type.
>
> An example is collections and arrays. If implemented properly, an array and
> a collection could be used interchangeably, although a collection may be
> preferred. For consistency, having the ability to dynamically cast from an
> array to a collection would be very useful.
>
> An idea of how this may look would be:
>
> <?php
>
> class Collection extends ...
> {
>      protected $items;
>
>      public function __construct(array $items)
>      {
>          $this->items = $items;
>      }
>
>     ...
>
>      public function __cast(array $items) : Collection
>      {
>          return new static($items)
>      }
> }
>
> --
>
> The __cast method MUST return an instance of itself, so that when called
> like so:
>
> function convert_me(Collection $collection)
> {
>      var_dump($collection);
> }
>
> convert_me([1,2,3]);
>
> the result there would be a Collection instance, instead of an array.
>
> If the type passed is not accepted by __cast() or __cast() throws an
> exception, then the current errors of invalid type are thrown, or perhaps
> the custom exception message.
>
> I'm not sure if this has been proposed before, and if it has, please could
> someone assist in me finding it, I couldn't find it by a quick search on
> the wiki.php.net/rfc page.
>
> Thanks.
> Alex.
>