7.8.1. Problem

7.8.2. Solution

class shape {
    function draw( ) {
        // write to screen
    }
}

class circle extends shape {
   function draw($origin, $radius) {
      // validate data
      if ($radius > 0) {
          parent::draw( );
          return true;
      }

      return false;
   }
}

7.8.3. Discussion

When you override a parent method by defining one in the child, the parent method isn't called unless you explicitly reference it.

In the Solution, we override the draw( ) method in the child class, circle, because you want to accept circle specific parameters and validate the data. However, in this case, we still want to perform the generic shape::draw( ) action, which does the actual drawing, so we call parent::draw( ) inside your method if $radius is greater than 0.

$circle = new circle;
if ($circle->draw($origin, $radius)) {
    $circle->parent::draw();
}

class circle extends shape {
    
    function circle( ) {
        $parent = get_parent_class($this);
        parent::$parent( );
    }
}

The call to parent::$parent( ) may look a little odd. However, PHP just substitutes in the parent class name for the $parent variable. Then, because there are ( ) s after the variable, PHP knows it should make a method call.

It's possible to hardcode the call to parent::shape( ) directly into the circle constructor:

function circle( ) {
    parent::shape( );
}

However, this isn't as flexible as using get_parent_class( ). It is faster, so if you know your object hierarchy isn't going to change, that may be a trade-off you can benefit from.

7.8.4. See Also