public function add(string $name, callable $callback): self
    {
        call_user_func($this->addCallback, $name, $callback);
        return $this;
    }
public function add(string $name, callable $callback): self
    {
        call_user_func($this->addCallback, $name, $callback);
        return $this;
    }
public function add ( string $ name , callable $ callback ) : self { call_user_func ( $ this -> addCallback , $ name , $ callback ) ; return $ this ; }
Creates a new shortcut.

@param string $name The name of the shortcut property.
@param callable $callback The callback to return the shortcut value.
@return self Returns a reference to itself.
Creates a new shortcut .