src/Payum/Core/Gateway.php
public function addExtension(ExtensionInterface $extension, $forcePrepend = false)
    {
        $this->extensions->addExtension($extension, $forcePrepend);
    }
public function addExtension(ExtensionInterface $extension, $forcePrepend = false)
    {
        $this->extensions->addExtension($extension, $forcePrepend);
    }
@param \Payum\Core\Extension\ExtensionInterface $extension
@param bool                                     $forcePrepend

@return void