class TwigReferenceFunctions

A helper used to unwrap TwigReference objects transparently.

This is providing a static magic function that makes it easier to unwrap TwigReference objects and pass variables by reference to show(), hide() and render().

The problem is that twig passes variables only by value. The following is a simplified version of the generated code by twig when the property "links" of a render array stored in $content should be hidden:

$_content_ = $content;
hide(getAttribute($_content_, 'links'));

As hide() is operating on a copy of the original array the hidden property is not set on the original $content variable.

TwigReferenceFunctions can be used in combination with TwigReference to solve this problem:

// Internally getContextReference returns the array wrapped in a
// TwigReference if certain criteria are met
function getContextReference(&$content) {
  $obj = new Drupal\Core\Template\TwigReference();
  $obj
    ->setReference($content);
  return $obj;
}

// [...]
// Simplified, generated twig code
$_content_ = getContextReference($content);
Drupal\Core\Template\TwigReferenceFunctions::hide(getAttribute($_content_, 'links'));

A TwigReference object is passed to the __callStatic function of TwigReferenceFunctions. The method unwraps the TwigReference and calls the hide() method essentially with a reference to $content['links'].

Therefore the hidden property is correctly set and a successive call to render() will not render the content twice.

Hierarchy

Expanded class hierarchy of TwigReferenceFunctions

See also

TwigReference

TwigReferenceFunction

TwigFactory

File

drupal/core/lib/Drupal/Core/Template/TwigReferenceFunctions.php, line 58

Definition of Drupal\Core\Template\TwigReferenceFunctions.

Namespace

class TwigReferenceFunctions {

  /**
   * Magic function to call functions called from twig templates with a
   * reference to the original variable.
   *
   * This checks if the array provided by value is containing a reference to
   * the original version. If yes it replaces the argument with its reference.
   *
   * @param $name
   *   The name of the function to call.
   * @param $arguments
   *   The arguments to process and pass to the called function.
   *
   * @return mixed
   *   Returns the output of the called function.
   *
   * @see TwigReference
   */
  public static function __callStatic($name, $arguments) {
    foreach ($arguments as $key => $val) {
      if (is_object($val) && $val instanceof TwigReference) {
        $arguments[$key] =& $val
          ->getReference();
      }
    }

    // Needed to pass by reference -- could also restrict to maximum one
    // argument instead
    $args = array();
    foreach ($arguments as $key => &$arg) {
      $args[$key] =& $arg;
    }
    return call_user_func_array($name, $args);
  }

}

Members

Name contains

Name does not contain

Type

Name	Modifiers	Type	Description	Overrides
TwigReferenceFunctions::__callStatic	public static	function	Magic function to call functions called from twig templates with a reference to the original variable.