Hi,
I would like to propose a new syntax that let's you implement an interface
only if it exists.
`class MyClass extends ?OptionalInterface {}`
If the `OptionalInterface` exists, the class implements it. If no such
interface can be found, it is ignored.
https://wiki.php.net/rfc/optional-interfaces
The need to declare compatibility with a certain interface without requiring
the interface itself comes up when you're writing code that should work with
various versions of other libraries or PHP itself and when a library
provides interoperability with some other library or a PHP extension, but
does not require it.
Although this would mainly be used by library developers, the consumers of
those libraries would also benefit as this syntax would clearly communicate
the intention of optional interoperability. IDEs and static analysis tools
could also have easier time with `?OptionalInterface` instead of class
definitions inside an `if (interface_exists(.)) { . } else {.}`.
I've not entirely sure about the naming as an "optional interface" feels
like an oxymoron. I've also considered names like non-required interfaces,
conditional interfaces, optional/conditional implementation or even soft
interfaces/soft implementation. Please let me know if the naming itself
bothers you.
Previous discussion: https://externals.io/message/125967
WIP implementation: https://github.com/php/php-src/pull/17288
Looking forward to your feedback and suggestions!
Juris
