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Date: Sat, 14 Aug 2021 12:19:30 -0400
Message-ID: <CAKuGYLSMY3WeUPe+LOBB_nSn3u-C_Pk3cnh0KDeKsSkjA7bTFQ@mail.gmail.com>
To: Jordan LeDoux <jordan.ledoux@gmail.com>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Never For Argument Types
From: matthewmatthew@gmail.com (Matthew Brown)

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Hey!

Using the "never" type to require that downstream libs specify a type does
not make intuitive sense to me, because the same is not true the other way
(covariantly) for return types.

The existence of a "never" type on an overriding method does not require
that upstream libs specify a return type =E2=80=94 this is perfectly valid:

class A {
  public function foo() {}
}
class AChild extends A {
  public function foo():never { exit; }
}

Best wishes,

Matt

On Fri, 13 Aug 2021 at 19:27, 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, `neve=
r`
> as the bottom type should indicate that implementing classes can require
> any type combination they want. This is in fact consistent with type theo=
ry
> 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 paramet=
er
> 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. I=
t
> 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 githu=
b
> repo to allow for easy contribution and collaboration.
>
> Any feedback is greatly appreciated.
>
> https://github.com/JordanRL/never-argument-type
>
> Jordan
>

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