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Date: Sun, 14 Mar 2021 17:01:41 +0100
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To: PHP internals <internals@lists.php.net>
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Subject: [RFC Proposal] Allow methods to 'become' static
From: gertp93@gmail.com (Gert de Pagter)

Hey Internals,

Recently i've been working on an older code base, where we have a lot
of classes with all
static methods. We've been moving to injecting the classes, and
calling the methods as if they
were not static.

I wanted to add interfaces to these classes, with non static methods,
so we can pretend in our implementation they are not static, and allow
us to easier switch to non static methods in the future.

This is (currently) not allowed by the language: https://3v4l.org/WKdvM
Is there any chance of this being possible in future versions of PHP?
This would only allow 'normal' methods to become static. Making static
methods non static would break Liskov substitution principle in PHP as
you may not be able to call the method in the same way. This means you
can't have a 'normal' method become static in an inherited class, and
then become 'normal' again in another inherited class. This works the
same way with co/contra-variance in return/parameter types:
(https://3v4l.org/j1SO9)