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Date: Sat, 07 Sep 2024 08:21:05 -0500
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Subject: Re: [PHP-DEV] bikeshed: Typed Aliases
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From: larry@garfieldtech.com ("Larry Garfield")

On Sat, Sep 7, 2024, at 7:42 AM, Mike Schinkel wrote:
>> 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? 
>
> 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.

Because it quickly can produce nonsensical syntax.

class A {}
class B {}

typealias AB: A|B;

// This is logically nonsensical.
class C extends AB {}

While there are edge cases where that might be logical (if A and B are interfaces and &-ed together, then it's kinda sorta the same as C implements A, B), separating those out and allowing just that subset sounds like a lot of work for dubious gain, and introducing surprise inconsistency.  Better to just avoid that entirely.

--Larry Garfield