multiple extends

[jjshell]

Hello,
still coding under PHP 4.

I have a few apps. There are some recursive methods. As my stuff is coded now, these methods are coded in each application. I would like to group them in one class and make this class the parent class of all the parent classes of my various applications.

Like:

class MainParent {

    //share all the methods common to all apps

}

class Application1 extends MainParent {

    //this class is the parent class of all the Application1 classes and contains the methods used by all the Application1 classes.

}

class Application2 extends MainParent {

    //this class is the parent class of all the Application2 classes  and contains the methods used by all the Application2 classes.

} 

I think that I'm good so far.

Now to what refers parent:: in the application subclasses? or $this-> ?

Like in:

class DoSomething extends Application2 {

    function DoSomething(){

        parent::sharedMethod();

    }

    function DoSomethingElse(){

        $var = $this->foo;

    } 

} 

thanks in advance

[AutisticCuckoo]

$this will refer to the instance itself, i.e., a DoSomething object.

parent refers to the parent class, i.e. Application2.

[jjshell]

Then how can reach the parent of the parent?

parent:: parent::sharedMethod();

?

[Scheisskopf]

$this will refer to the instance itself

This is correct, but a subclass is a type of parent, so $this->sharedMethod() should work i.e.

<?

class basebase {
    function speak()
    {
        print "hello";
    }
}

class base extends basebase { }

class child extends base {
    function child()
    {
        $this->speak();
    }
}

$c = new child();

?>

prints "hello"

[Forbes]

I've used this method for a calendar class; Calendar parent class which is extended by Day, Week and Month classes.

It's worth noting that you will have some fun with include() and require() functions calls...

[AutisticCuckoo]

Then how can reach the parent of the parent?

parent:: parent::sharedMethod();

?

MainParent::sharedMethod(); 

As Scheisskopf noted, you don't have to specify that the method is defined in a parent class unless you've overridden it in a subclass and need to specify that it's the base class version you want.

I.e., unless you override sharedMethod() in Application2 and/or DoSomething, you can simply call it like this:

$this->sharedMethod(); 

[jjshell]

Thanks for your replies.
I searched php.net for MainParent:: but couldn't find anything about it... Do you have some reference about it?

[Scheisskopf]

It's worth noting that you will have some fun with include() and require() functions calls...

That's where the autoload function comes in handy.

@jjshell: I suspect that MainParent is a made up class

[dreamscape]

"MainParent" is the name of the parent parent's class.

If you don't want to statically call it by name, you can just pass it up the chain too.

<?php

class MainParent { 

    function sharedMethod() {
        echo 'MainParent::sharedMethod()';
    }

} 

class Application2 extends MainParent { 

    function sharedMethod() {
        parent::sharedMethod();
    }

}


class DoSomething extends Application2 { 

    function DoSomething() {
        parent::sharedMethod();
    }

    function DoSomethingElse() {
        $var = $this->foo;
    }

}

$doit = new DoSomething();

outputs:

MainParent::sharedMethod()

[AutisticCuckoo]

Thanks for your replies.
I searched php.net for MainParent:: but couldn't find anything about it... Do you have some reference about it?

class MainParent { 

    //share all the methods common to all apps 

} 

It's what you called your top-level base class.

[McGruff]

"Application" classes are almost certainly trying to do too much. I think you'll need to split this up into smaller, more focussed classes with discrete roles.

Once you've encapsulated everything nicely you then need to figure out how to get everything talking to each other... Studying design patterns will help to give you some ideas. Inheritance is definitely not the way to do this and should be reserved for situations where the two classes are basically the same thing.

[jjshell]

What patterns could fit?

[jjshell]

Is it the same with variables? Are they all shared? I seem to have a hard time getting them...

class MainParent { 

  var $var;

  function MainParent()
  {

      $this->var = 'foo';

  }

} 


class Application extends MainParent { 

} 

class DoSomething extends Application { 


    function DoSomethingElse(){ 

        return $this->var;

    } 

} 

the output of DoSomethingElse should be 'foo' right?

[McGruff]

You must explicitly call a parent constructor, eg:

class DoSomething extends Application 
{
    function DoSomething(){
        $this->MainParent();
    }
    function DoSomethingElse(){
        return $this->var;
    }
    // etc 

[McGruff]

What patterns could fit?

OOP design takes a while to get to grips with. Patterns give you some ideas about how to weave objects together but you wouldn't code to fit a pattern: you fit the patterns to your requirements. The key point is to create objects with clearly defined responsibilities which don't try to do too much.

If you're starting out with OOP you won't get it right first time - even experienced programmers won't get it right first time. It's a kind of evolutionary process. The forces of (un)natural selection are questions such as are the objects too tightly coupled? Are they cohesive? What happens if you stress the design with a certain type of change such as a switch to a different database? If you're testing, the bottom line is do the unit & etc tests run green?

It's a strange mix of philosophy and engineering. You're free to invent your own entities to carry out particular roles although they also have to relate closely to practical requirements. You'll get killed in programming with any lack of clarity all the way from variable and method names right up to the top level client requirements and the first step is to identify exactly what your requirements are then code to these. Modern practices like Extreme Programming put a strong emphasis on clear requirements and use testing to stay focussed on these.

http://c2.com/cgi/wiki?CouplingAndCohesion
http://www.developerspot.com/tutoria...ent/page1.html

[BerislavLopac]

You must explicitly call a parent constructor

Only if you override it with the subclass constructor. Otherwise the parent class contructor is called automatically -- jjshell's code works perfectly:

class MainParent
{
    var $var;

    function MainParent()
    {
        $this->var = 'foo';
    }
}


class Application extends MainParent
{
}

class DoSomething extends Application
{
    function DoSomethingElse(){
        return $this->var;
    }
}


$test = new DoSomething();
echo $test->DoSomethingElse(); 

[McGruff]

Oops my mistake. I got mixed up with all those DoSomething's.

[Forbes]

OOP design takes a while to get to grips with. Patterns give you some ideas about how to weave objects together but you wouldn't code to fit a pattern: you fit the patterns to your requirements. The key point is to create objects with clearly defined responsibilities which don't try to do too much.

If you're starting out with OOP you won't get it right first time - even experienced programmers won't get it right first time. It's a kind of evolutionary process. The forces of (un)natural selection are questions such as are the objects too tightly coupled? Are they cohesive? What happens if you stress the design with a certain type of change such as a switch to a different database? If you're testing, the bottom line is do the unit & etc tests run green?

It's a strange mix of philosophy and engineering. You're free to invent your own entities to carry out particular roles although they also have to relate closely to practical requirements. You'll get killed in programming with any lack of clarity all the way from variable and method names right up to the top level client requirements and the first step is to identify exactly what your requirements are then code to these. Modern practices like Extreme Programming put a strong emphasis on clear requirements and use testing to stay focussed on these.

http://c2.com/cgi/wiki?CouplingAndCohesion
http://www.developerspot.com/tutoria...ent/page1.html

I'd second much of that .. if not all!

I took quite a while to warm to object-oriented PHP.

In fact, for a while, I was doin' it while not diggin' it!

In the end, the immediate benefits were much tidier code, which meant more manageable structure, which meant saved time .. which meant saved money.

Eventually, many more benefits come to fore...

[jjshell]

The mainparent class isn't instantiated... maybe that's why why I can't get it? It's like the Application class can use the vars set in MainParent but not DoSomething...
Does anyone have an idea why? Any usual suspect around?

[AutisticCuckoo]

The example you posted works exactly as it is. I pasted your code into an editor and added two lines:

$foo = new DoSomething();
echo $foo->DoSomethingElse(); 

The result, when I ran it, was:

foo

[jjshell]

Ok fine... Got it.

Now please take a look at that scenario:

//MainParent() is never instantiated 
class MainParent { 

  var $var; //var should be available to all the children 
  var $bar; //bar should be available to all the children 

  function MainParent() 
  { 

      $this->bar = 'bar'; 

  } 

} 


class Application extends MainParent { 

  var $doSomething;
  
  function Application() 
  { 

      $this->var = 'foo'; 
      $this->doSomething = new DoSomething(); 
      
  }
  
  function getVar()
  {
  
      return $this->doSomething->returnVar();
  
  }
  
  function getBar()
  {
  
      return $this->doSomething->returnBar();
  
  } 
  
  
  

} 

class DoSomething extends MainParent { 

  function DoSomething() 
  { 

      parent::MainParent(); 

  } 

  function returnVar() 
  { 

        return $this->var; 

  } 

  function returnBar() 
  { 

        return $this->bar; 

  } 

} 

$foo = new Application(); 
echo $foo->getVar(); 
echo $foo->getBar(); 

I can get $bar but not $var... how come?

thank you all so much for your support and patience by the way

[BerislavLopac]

I can get $bar but not $var... how come?

Constructors sorta bubble up the inheritance hierarchy. The interpreter looks for a constructor in the instantiated class; if it doesn't find it there, it looks in its parent class, and so on. As soon as it finds one, the interpreter executes it and stops looking.

[AutisticCuckoo]

You need to call the base class constructor in Application's constructor, since you supply an explicit constructor (base class constructors are only called implicitly if there is no explicit constructor in the derived class).

  function Application() 
  { 

      // call the base class constructor
      $this->MainParent();

      $this->var = 'foo'; 
      $this->doSomething = new DoSomething(); 
       
  } 

[jjshell]

Great Tommy!

thanks