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Subject: Re: [PHP-DEV] bikeshed: Typed Aliases
In-Reply-To: <928A2984-6035-4DA6-9EA7-12E85237C270@php.net>
Date: Sat, 7 Sep 2024 08:42:21 -0400
Cc: Rob Landers <rob@bottled.codes>,
 PHP internals <internals@lists.php.net>
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Message-ID: <71DEAAB9-D788-4EB9-A07F-E47211F92F78@newclarity.net>
References: <0fa39535-f22d-4eba-b4df-90abe39e683a@app.fastmail.com>
 <e73be2b0-faa9-42eb-a9f6-8308cf4f8c94@app.fastmail.com>
 <ed3847bf-af2e-4e33-ac09-66e44696fdeb@app.fastmail.com>
 <79e58673-50ec-461e-a998-736b020e4287@app.fastmail.com>
 <a3cd6d90-cfac-40d5-a59a-c9f6d9dbe5f0@app.fastmail.com>
 <928A2984-6035-4DA6-9EA7-12E85237C270@php.net>
To: Davey Shafik <davey@php.net>,
 Larry Garfield <larry@garfieldtech.com>
From: mike@newclarity.net (Mike Schinkel)

> On Sep 6, 2024, at 4:45 PM, Larry Garfield <larry@garfieldtech.com> =
wrote:
> Aliases can then be used only in parameter, return, property, and =
instanceof types.  Extends and implements are out of scope entirely.

Is there a strong technical reason why extends and implements should be =
out of scope?=20

There is definite utility for this, to create a local alias in a =
namespace that can be used throughout the namespace rather than having =
to refer to the external namespace in many different places.

> On Sep 6, 2024, at 8:46 PM, Davey Shafik <davey@php.net> wrote:
> I would very much prefer to either go all in with an Enum-like (which =
means that we can hang methods on to the value) or we need to =
distinguish between type hints for class-likes and type hints for =
not-class-likes (*Bar anyone?).

Allowing methods also have definite value as most use-cases I have seen =
in other languages alias in order to add methods, especially for =
enabling support of interfaces.

Which, however, brings up an important distinction that other languages =
have made and which I think PHP would benefit from addressing:

1. Type Alias =3D> Different Name for Same Type
2. Type Def =3D> New Type which has all the same properties and methods =
of other type

e.g. (being hypothetical with the syntax; bikeshed away):

typealias  LocalWidget: Widget

typedef  MyWidget: Widget {
   function foo() {...}
}

function doSomething(Widget $widget) {...}

$w =3D new LocalWidget;
doSomething($w);           // This works, no problem as LocalWidget =3D=3D=
=3D Widget

$w =3D new MyWidget;
doSomething($w);           // This throws an error as MyWidget !=3D=3D =
Widget

-Mike