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Date: Tue, 27 Nov 2018 14:14:43 -0700
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To: Larry Garfield <larry@garfieldtech.com>
Cc: internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC][Discuss] Covariant return- and contravariant
 parameter- types
From: levim@php.net (Levi Morrison)

On Tue, Nov 27, 2018 at 2:00 PM Levi Morrison <levim@php.net> wrote:
>
> On Tue, Nov 27, 2018 at 11:36 AM Larry Garfield <larry@garfieldtech.com> wrote:
> >
> > On Monday, November 26, 2018 3:25:52 PM CST Levi Morrison wrote:
> > > I am happy to announce my latest RFC, [Covariant Returns and
> > > Contravariant Parameters][1], is open for discussion. If you do not
> > > recognize those terms then hopefully the introduction coupled with the
> > > [examples][2] will help. Here is one snippet that demonstrates
> > > covariant return types:
> > >
> > > <?php
> > > interface Repository {
> > >   function fetch(int $id): ?Entity;
> > > }
> > >
> > > class UserFactory implements Repository {
> > >   function fetch(int $id): ?UserEntity {
> > >     /* Since UserEntity is an Entity, this is now allowed */
> > >     /* ... implementation ... */
> > >   }
> > > }
> > > ?>
> > >
> > > Covariant return types and contravariant parameter types are highly
> > > requested features; here are a few of the bug reports:
> > >
> > >   * https://bugs.php.net/bug.php?id=71825
> > >   * https://bugs.php.net/bug.php?id=72442
> > >   * https://bugs.php.net/bug.php?id=75385
> > >   * https://bugs.php.net/bug.php?id=75823
> > >
> > > There is a [preliminary implementation][3] that is available. It will
> > > not be rebased during discussion to allow people to check out the code
> > > and get updates without worrying about it breaking. The code quality
> > > can definitely be improved, and there are still a few todo comments in
> > > the code.
> > >
> > > Please do not discuss the items found in [Future Scope][4] as part of
> > > this thread, which includes discussing types such as `mixed`,
> > > `scalar`, `numeric`, etc.
> > >
> > > I look forward to your feedback, and especially with your
> > > experimentation with the implementation.
> > >
> > > Levi Morrison
> > >
> > >   [1]:
> > > https://wiki.php.net/rfc/covariant-returns-and-contravariant-parameters
> > > [2]:
> > > https://wiki.php.net/rfc/covariant-returns-and-contravariant-parameters#exa
> > > mples [3]:
> > > https://github.com/php/php-src/compare/master...morrisonlevi:variance2 [4]:
> > > https://wiki.php.net/rfc/covariant-returns-and-contravariant-parameters#fut
> > > ure_scope
> >
> > Looks like fun!
> >
> > Would this also include allowing a return type of `static`, which would be
> > useful for the "Return the object that was invoked" case or "return a new
> > instance of the same object" case?  Currently we're limited to `return self`,
> > which is, of course, not the same thing and less flexible.
> >
> > --Larry Garfield
>
> It does not. To be honest, I did not think of it until your question.

After thinking about it, I believe it is out of scope for this RFC.
While `static` would be covariant, it's also more than that.
Accordingly, it deserves to have its own consideration and voting.