src/Payum/Core/Gateway.php
public function addAction(ActionInterface $action, $forcePrepend = false)
    {
        $forcePrepend ?
            array_unshift($this->actions, $action) :
            array_push($this->actions, $action)
        ;
    }
public function addAction(ActionInterface $action, $forcePrepend = false)
    {
        $forcePrepend ?
            array_unshift($this->actions, $action) :
            array_push($this->actions, $action)
        ;
    }
@param Action\ActionInterface $action
@param bool                   $forcePrepend

@return void