named.php

<?php

interface NamedCallback {
    public function __invoke(string $foo, bool $bar): string;
}

function func(NamedCallback $cb) {
    var_dump($cb("Hello", true));
}

func(new class implements NamedCallback {
    public function __invoke(string $foo, bool $bar): string {
        return $bar ? strrev($foo) : $foo;
    } 
});