gistfile1.php

// original code
public function getFunctions()
{
    return array(
        new \Twig_SimpleFunction('show_source_code', array($this, 'showSourceCode'), array('is_safe' => array('html'), 'needs_environment' => true)),
    );
}

// new code
public function getFunctions()
{
    return array(
        'show_source_code' => new \Twig_Function_Method(array($this, 'showSourceCode'), array('is_safe' => array('html'), 'needs_environment' => true)),
    );
}