Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:120582
MIME-Version: 1.0
Reply-To: Levi Morrison <levi.morrison@datadoghq.com>
Date: Wed, 14 Jun 2023 21:47:40 -0600
Message-ID: <CAAKU0umNOJ+6x44WRuzc2e9_5sDehAq5UB_aFn+cT4wxTny9wg@mail.gmail.com>
To: PHP internals <internals@lists.php.net>
Content-Type: text/plain; charset="UTF-8"
Subject: [RFC] Interface Default Methods
From: internals@lists.php.net ("Levi Morrison via internals")

Hello, PHP Internals,

I am moving my RFC for interface default methods to discussion:
https://wiki.php.net/rfc/interface-default-methods.

This can be a useful tool for a few reasons:
 1. It can make implementing an interface easier when certain methods
can be implemented by other methods in the interface. For example, if
`Countable` had an `isEmpty(): bool` method, it could be implemented
by doing `$this->count() > 0`. Of course, if an implementation can be
more efficient, they are still free to implement it how they want.
 2. It can mitigate BC breaks in some cases. It's somewhat common for
authors to want to expand new methods onto existing interfaces over
time. Although this would still be a BC break, it moves it from a
massive change (every single implementor must add something, even if
it's a stub, or it will fail to compile) to a naming collision issue
only (only classes which already had a method of the same name will
fail to compile).

There is prior art for this feature in both Java and C#. There may be
other languages, but I was aware of at least these.

Note that the RFC links to a partial implementation. If there are two
or more interfaces with default methods of the same shape (name, args,
etc) and a class implements both interfaces and doesn't provide a
concrete implementation, which default implementation should be
chosen? There is a proposal for resolving this in some cases which is
modelled after Java's implementation, but it isn't implemented.

Thank you for your time. I look forward to productive feedback.

Levi Morrison