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Date: Tue, 23 Apr 2019 12:26:40 +0300
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Subject: Re: [PHP-DEV] Object Type Casting Reloaded
From: php@hristov.com (Andrey Hristov)

  Hi,
maybe with short closures this will be pretty easy to implement by 
injecting a short closure that expects the return type to be of the type 
to be casted and to return it.

Something in the like of :

$service = (fn(EmailService $s):EmailService => $s 
;)($diContainer->get('email.service'));

Not that I support pulling services from a container most often being an 
anti-pattern.

Cheers,
Andrey

On 23.04.19 г. 0:47 ч., Benjamin Morel wrote:
> Hi internals,
> 
> I'd like to revive an old discussion <https://externals.io/message/67131> about
> object type casting.
> 
> The idea would be to allow (ClassName) casting:
> 
>      $service = (EmailService) $diContainer->get('email.service');
> 
> The above code would throw a TypeError if the value is not an instance of
> the given class. I see the following advantages:
> 
> - Type safety: we can be sure that the value is of the correct type or that
> we'll get an Error. This syntax allows to fail early if the variable
> happens to not be of the expected type, and avoids much more verbose checks;
> - Static analysis: IDEs and static code analysis tools can now understand
> the type of the variable, without having to resort to `@var` annotations.
> 
> These combine into a third advantage: readability. Today's equivalent of
> the above one-liner could be:
> 
>      /** @var EmailService $service */
>      $service = $diContainer->get('email.service');
>      if (! $service instanceof EmailService) {
>          throw new TypeError('Expected instance of EmailService, ...');
>      }
> 
> Which is a lot of boilerplate code that could be easily avoided by
> introducing this new syntax.
> 
> Before moving forward and working on a formal RFC, I'd like to hear your
> thoughts: what's your early feeling about this? Did I miss other
> discussions around this subject? Are there any technical issues that come
> to mind? Could this feature help the upcoming JIT compiler produce more
> efficient machine code by knowing the type of the variable at compile time?
> etc.
> 
> Note: "casting" might not be the perfect name here as what we're really
> doing is a type check, but this reuses the type casting syntax and
> resembles Java's object casting.
> 
> Thank you,
> Ben
>