// How am I supposed to call this correctly?
    // I want to be free to use closures for c1::cb...

    function f1()
    {
        echo "1";
    }

    class c1
    {
        public $cb = f1;
        public function callcb()
        {
            // this works:
            $cb = $this->cb;
            $cb();
            // the following versions don't:
            $this->cb(); // Call to undefined method c1::cb()
            ${$this->cb}(); // Function name must be a string (this is the one which IMO really should work)
            $this->$cb(); // Function name must be a string (even though I expected it to resolve to c1::f1 and fail because of that
            $this->{$this->cb}(); // Call to undefined method c1::f1
            {$this->cb}(); // } unexpected (obviously)
            ${this->cb}(); // unexpected T_OBJECT_OPERATOR

            // Note: variants 2 and 3 don't work even with public $cb='f1'.
        }
    }
    $c = new c1;
    $c->callcb();
    $page->end();