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.led...@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
