Partial Function Application for instance of non-static methods ("$this")

[arnaud-lb]

RFC: https://wiki.php.net/rfc/partial_function_application_this

[TimWolla]

Can you also include:

<?php
class Foo {
    public function dump(...$args) {
        var_dump($args);
    }
}
$f = Foo::dump(this: ?, ...);
$f(new Foo(), ...['this' => 'foo']);

as a test to make it clear that this: and 'this' unpacking can be combined?

[TimWolla]

If possible the error message could be clearer here:

The 'this' placeholder may only be used on methods

or similar. I'll check existing error messages for a proper suggestion if/when the RFC passes.

[TimWolla]

Similarly:

The 'this' parameter must be a placeholder

[bwoebi]

./sapi/cli/php -r 'class A { function b() { var_dump($this); } } $cb = A::b(this: ?); $next = $cb(this: ?); $next(new A);'

Fatal error: Invalid use of 'this' placeholder in Command line code on line 1
Stack trace:
#0 {main}

this should probably not fail.

This comes from the rename of this to __this, which is ... odd. I know the RFC acknowledges this, but it's really odd.
I'm aware that this comes from the implementation, but does it have to be that way?

Would it be possible to introduce a fallback instead, whereby this becomes a normal named parameter, when the callee is not a reference to a non-static method? I.e. add a slow-path with some specialized logic in zend_partial_create which moves this around?

[arnaud-lb]

Yes it's a compromise to avoid adding special cases in the engine to support $this as parameter name or variable name.

What we could probably do, is to set the param name to this in arginfo, after compilation, so that a PFA compiled as fn($__this) => $__this->fn() would be seen as a fn($this) from the outside.