Not sure i get what you mean. With "abstract functions" I include also
those in interfaces.
I haven't tried 7.2 yet, but i think what I'm proposing is already
supported (+ kelunik's RFC):
```
interface A{
function x(stdClass $foo);
}
interface B extends A{
function x($foo): stdClass;
}
`
An abstract function is a partial interface: I see no value in adding
exceptions to interface implementations, especially if you add that:
* only works with abstract classes, not interfaces
* has a too narrow use-case scenario (need more necessity and scenarios
with common patterns)
* just writ
