How do I call PHP parent methods from within an in

Question

In PHP, I'm trying to reference a method defined in an object's parent class, from a method inherited from the object's parent class. Here's the code:

class base_class {
  function do_something() {
    print "base_class::do_something()\n";
  }
  function inherit_this() {
    parent::do_something();
  }
}
class middle_class extends base_class {
  function do_something() {
    print "middle_class::do_something()\n";
  }
}
class top_class extends middle_class {
  function do_something() {
    print "top_class::do_something()\n";
    $this->inherit_this();
  }
}

$obj = new top_class;
$obj->do_something();

The problem is that parent::do_something() in inherit_this() tries to find the parent class of base_class, not the parent of the object's actual class, and the example above throws an error. Is there something I can write instead of parent::do_something() that would call middle_class::do_something(), and that would still work even in classes that extend (say) top_class?

Answer 1

I'll start by saying "Thank you" to grrbrr404. He gave me some ideas and got me started in the right direction.

The solution I finally settled on was the following:

function inherit_this() {
  $bt = debug_backtrace();
  call_user_func(array($this, get_parent_class($bt[1]['class']) . '::do_something'));
}

It's not pretty (I particularly hate calling debug_backtrace() for this), but it keeps the object context set to $this, and handles the case where the method is called from a method somewhere in the middle of the object hierarchy.

For those who found my example confusing and/or wanted to know "Why would you want to do this?" I apologize, and provide the following additional example, which is hopefully more illustrative and closer to the original problem. It is considerably longer, but hopefully shows why I care about keeping $this set properly, and also shows why I can't hard-code any particular class name or use $this->method(). Avoiding infinite loops is always a priority with me. :-)

class class1_required_type { }
class class2_required_type { }
class class3_required_type { }
class class4_required_type { }

class class1 {
  protected $data = array();
  protected function checkType($name, $value, $requiredType) {
    print "In class1::checkType()\n";
    if (get_class($value) === $requiredType) {
      $backtrace = debug_backtrace();
      call_user_func(array($this, get_parent_class($backtrace[1]['class']) . "::mySet"), $name, $value);
    } else {
      throw new Exception(get_class($this) . "::mySet('" . $name . "') requires an object of type '" . $requiredType . "', but got '" . get_class($value) . "'");
    }
  }
  function mySet($name, $value) {
    print "In class1::mySet()\n";
    if ($name === 'class1_field') {
      $this->checkType($name, $value, 'class1_required_type');
    } else {
      $this->data[$name] = $value;
    }
  }
  function dump() {
    foreach ($this->data as $key => $value) {
      print "$key: " . get_class($value) . "\n";
    }
  }
}

class class2 extends class1 {
  function mySet($name, $value) {
    print "In class2::mySet()\n";
    if ($name === 'class2_field') {
      $this->checkType($name, $value, 'class2_required_type');
    } else {
      parent::mySet($name, $value);
    }
  }
}

class class3 extends class2 {
  function mySet($name, $value) {
    print "In class3::mySet()\n";
    if ($name === 'class3_field') {
      $this->checkType($name, $value, 'class3_required_type');
    } else {
      parent::mySet($name, $value);
    }
  }
}

class class4 extends class3 {
  function mySet($name, $value) {
    print "In class4::mySet()\n";
    if ($name === 'class4_field') {
      $this->checkType($name, $value, 'class4_required_type');
    } else {
      parent::mySet($name, $value);
    }
  }
}

$obj = new class4;
$obj->mySet('class3_field', new class3_required_type);
$obj->dump();

I'm trying to avoid duplication of the "checkType()" function, yet still provide correct behavior even when the hierarchy gets arbitrarily large.

More elegant solutions are, of course, most welcome.

Answer 2

class base_class {
  function do_something() {
    print "base_class::do_something()\n";
  }
  function inherit_this() {
   //parent::do_something();
     $class = get_called_class();
     $class::do_something();
  }
}

Answer 3

Im not quite sure I understands why you want to do like this. But I guess you cannot do it. I understand that you will be able to make a middle_class2 and be able inherit from that, and then it would be middle_class2 instead of middle_class's dosomething you call?!

So I guess you'll need to create the

  function inherit_this() {
    parent::do_something();
  }

in the middle_class.

I thought about a get_class($this)::parent::do_something().. but that didn't work.

Just to be sure.. You want to call middle_class::do_something() right??

Answer 4

To get it work you can modify your base_class like this:

class base_class {
  function do_something() {
    print "base_class::do_something()\n";
  }

 function inherit_this() {
    $this->do_something();
 }
}

Then your top_clas will call inherit_this() of your base class, but there will be a recursion: do_something() of top_class calls $this->inherit_this(), and in base_class you call again $this->do_something() (in your base class $this will reference to your top_class). Because of that, you will call inherit_this() over and over again.

You should rename the methods to prevent that.

Update

If you want that base_class inherit_this() prints "base_class::do_something" you could modify your base_class like this:

class base_class {
  function do_something() {
    print "base_class::do_something()\n";
  }

  function inherit_this() {
     base_class::do_something();
  }

}

In this case you make a static call to the base_class method do_something(). The output is top_class::do_something() base_class::do_something()

Update 2

Regarding to your comment you can modify your base_class like this:

class base_class {
  function do_something() {
    print "base_class::do_something()\n";
  }
  function inherit_this() {    
    $par = get_parent_class($this);
    $par::do_something();
  }
}

You get the parrent class of $this and then call the method. Output will be: top_class::do_something() middle_class::do_something()