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Date: Wed, 8 May 2024 14:51:26 +0200
Message-ID: <CAB-BujbiFJW1gDrF=nW5Mo0sPvpObN+5NQ2PEonrPDsyGwiTUA@mail.gmail.com>
Subject: Re: [PHP-DEV] [RFC] Never For Argument Types
To: Jordan LeDoux <jordan.ledoux@gmail.com>
Cc: PHP internals <internals@lists.php.net>
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From: andreas@dqxtech.net (Andreas Hennings)

Hello list,
to revive this old RFC.

One really nice application of never parameters is with intersection types:

interface I {}

interface ReturnI {
    public function foo(never $x): I;
}

interface AcceptI {
    public function foo(I $x): mixed;
}

function f(ReturnI&AcceptI $arg, I $x): I {
    return $arg->foo($x);
}

Look at a live example where I simulate the "never" with an
"AlmostNever" interface.
https://3v4l.org/dPbgt
It can even be applied with additional parameters:
https://3v4l.org/l8eG6

An application can use this to reduce the range of individual
interfaces, and cover scenarios that would otherwise require generics
or callable types.

So.. I would really like to see it :)

--- Andreas



On Sat, 14 Aug 2021 at 01:27, Jordan LeDoux <jordan.ledoux@gmail.com> wrote:
>
> Hey internals,
>
> I've been working on the draft for my operator overloading RFC, and in
> doing so I encountered a separate change that I would like to see.
>
> That is, the use of `never` as an argument type for interfaces. Since
> arguments in PHP are contravariant to preserve Liskov substitution, `never`
> as the bottom type should indicate that implementing classes can require
> any type combination they want. This is in fact consistent with type theory
> and set theory, and is how the bottom type is treated in several other
> languages.
>
> In this case, the bottom type would be used to indicate covariant parameter
> polymorphism while not conflicting with LSP.
>
> This would provide a sort of minimal form of generics to PHP without the
> issues that actual generics present from an implementation perspective. It
> would not, however, restrict or hinder any future RFC for generics.
>
> This is at the first draft stage, and I currently have the RFC on a github
> repo to allow for easy contribution and collaboration.
>
> Any feedback is greatly appreciated.
>
> https://github.com/JordanRL/never-argument-type
>
> Jordan