src/Console/Output/ConsoleOutput.php
public function once($event, callable $listener)
    {
        parent::once($event, $listener);
        $this->stderr->once($event, $listener);
    }
public function once($event, callable $listener)
    {
        parent::once($event, $listener);
        $this->stderr->once($event, $listener);
    }
public function once ( $ event , callable $ listener ) { parent :: once ( $ event , $ listener ) ; $ this -> stderr -> once ( $ event , $ listener ) ; }
Helper method to proxy event listeners to the wrapped stream.

@param $event
@param callable $listener
Helper method to proxy event listeners to the wrapped stream .