A spike for having CallableInterfaces in PHP

callable-interface.php

<?php

// In PHP internals, maybe this is an abstract class instead?
// Maybe an attribute?
#[Attribute]
class FunctionalInterface {}

#[FunctionalInterface]
interface MyAction {
    
    public function invoke(string $foo, int $bar) : bool;
    
}

class ObjectAction implements MyAction {
    
    public function invoke(string $foo, int $bar) : bool {
        echoo $foo, $bar;
        return true;
    }
    
}


function doIt(MyAction $action) {
    $action->invoke('foo', 42);   
}

$goodFunc = function(string $a, int $b) : bool { 
    echo $b, $a;
    return true;
};
$badFunc = function() {};

doIt(new ObjectAction());       // 'foo', 42
doIt($goodFunc);    // 42, 'foo' 
doIt($badFunc);    // exception, wrong method signature