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Date: Tue, 14 Aug 2012 10:46:26 +0300
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Subject: Inline typecasting / typehinting for classes and interfaces
From: sv_forums@fmethod.com ("Stan Vass")

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I've felt the need for this for some time.

Proposed syntax:
-------------------------

$x =3D (InterfaceName) $container->service;

Proposed behavior:
---------------------------

Checks if the instance if an instance of the given class/interfaces. If =
yes, does nothing, if not, issues a fatal error. Pseudo code:

$temp =3D $container->service;
if ($temp instanceof InterfaceName) {
    $x =3D $temp;
} else {
    trigger_error('The object can not be cast to InterfaceName');
}

Use cases:
----------------

As my example hints, the intent is to provide type safety and hinting =
for the increasingly used dependency injection container pattern.=20

It's useful to provide type safety also for all similar patterns which =
may not return a result of the expected type: Registry, ServiceLocator, =
Factory etc.

Additionally to runtime type safety, this will also serve to =
editors/IDEs as an inline hint to provide proper autocompletion, i.e. =
instead of this:

/** @var $foo InterfaceName */
$foo =3D $container->service;

People can now just write:

$foo =3D (InterfaceName) $container->service;

Alternative syntax:
--------------------------

I realize "casting" isn't a perfect match as the behavior is equivalent =
to inline type hinting. On the other hand, casting and inline type =
hinting in dynamic languages often behave identically (see the casting =
behavior in ActionScript which combines type hints with a JS-like =
dynamic type system).

And this syntax doesn't introduce new keywords. Still, alternative ways =
to implement this could be:

1. $foo =3D $container->service as InterfaceName;
2. $foo =3D $container->service is InterfaceName;
3. $foo =3D (InterfaceName $container->service);
4. InterfaceName $foo =3D $container->service;

All of those would be fine, especially 4, which has precedent in other =
languages, and in PHP as well with typehinting and in catch blocks:  =
catch (ClassName $e) { ... }

I'm ok with suggestions for any syntax that is as short, if it fits the =
behavior better.

Feedback?

Stan
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