Type-dispatch methods

Rationale

Code simplification.

Instead of having one method with a big if / else block inside, we will allow declaring separate methods, each with their type literals embedded.

Declaration

Current:

  public function setXml($xml) {
    if ($xml instanceof Tree) {
      // A
    } else if (is_string($xml)) {
      // B
    }
  }

New:

  public function setXml·Tree($xml) {
    // A
  }

  public function setXml·þstring($xml) {
    // B
  }

Dispatch

Dispatch will be performed at runtime, except if a compiler / code preprocessor can determine exactly.

Here's an example of a generated dispatcher method:

  #[@dispatch]
  public final function setXml() {
    static $overloads= array(
      1 => array(
        'setXml·Tree'    => array('!Tree'),
        'setXml·þstring' => array('!string'),
      ),
    );

    $args= func_get_args();
    foreach (@$overloads[sizeof($args)] as $method => $signature) {
      foreach ($signature as $i => $literal) {
        if (NULL === $args[$i]) {
          if ('!' === $literal{0} || !strstr($literal, '.')) continue 2;
        } else {
          if (!Type::forName(substr($literal, 1))->isInstance($args[$i])) continue 2;
        }
      }
      return call_user_func_array(array($this, $method), $args);
    }

    raise(
      'lang.MethodNotImplementedException', 
      'No overload for ['.implode(', ', array_map(array('xp', 'typeOf'), $args)).']',
      'setXml'
    );
  }

Reflection

Reflection will list one method, "setXml" in this case. A reflective invocation will also apply dispatch logic.

n/a

TODO

RFC #0197

• http://experiments.xp-forge.net/xml/browse?arena,rfc0195 Experiment

<EOF>