[RESOLVED] OO: Turning parent into child...

[Banacek]

Question: say I have the following code:

class Parent
{
     private $name;
     private $email;

 public function Parent()
 {
      $this->name = "Bob";
      $this->email = "[e-mail]";
 }
}

class Child extends Parent
{
     public function test()
     {
          //something here...
     }
}

Now, if I have a Parent object already created, what is the best way to turn that object into a Child object, so that it would have the same name and email, but have the Child functions? Thanks!

[banzaimonkey]

Hm... I think what you may want to do is pass the name and e-mail into the constructor function. When you create a new parent object, it will have the name and e-mail given to it by the constructor, and then this will be appropriated by the child class.

If my understanding of OOP is correct, the child class will already have innate access to the name and e-mail data by virtue of inheritance, as well as all parent functions, variables, etc.; all you need to do is structure your classes in such a way that the data initialization in the parent is dynamically, rather than statically, defined.

For example (not syntactically correct):

class Parent
{
  private $name;
  private $email;

  public function Parent($input1, $input2)
  {
    $name = $input1;
    $email = $input2;
  }

  public function whateverParentDoes()
  {
    print();
    dance();
    make_money();
    sing_songs();
  }
}

class Child extends Parent
{
  public function sendEmail()
  {
    sendemailto($name);
  }
}

Then when you call your parent, you'd have something like:

$parent1 = new Parent($name, $email);

This will pass the name and e-mail into the function when it is created, allowing for non-static data.

As I said, and I apologize, the code is nowhere near any sort of syntactical correctness, and I may have incorrectly explained things (it's been about two years since I took a class on OOP (in Java, to boot) and I haven't used it in the mean time). If that doesn't get you squared away, someone else will probably come along and correct my mistakes. Wikipedia has an article on OOP, too, including a PHP example. 😉

[Banacek]

banzaimonkey wrote:

If my understanding of OOP is correct, the child class will already have innate access to the name and e-mail data by virtue of inheritance, as well as all parent functions, variables, etc.; all you need to do is structure your classes in such a way that the data initialization in the parent is dynamically, rather than statically, defined.

You might be misunderstanding what I'm looking to do 🙂 Using the code above, I write the following:

<?php
include ("class.php");

$user = new Parent();

/*code to check and see if $user is in system or something

find out it's valid, then turn $user into a Child Object, so it can use those functions.*/

This of course is a very simplified version, but the question is the same. I hope this helps.

EDIT: I thinking about passing the parent object through when I create the child class. As in:

class Child extends Parent
{
     public function Child($parent)
     {
          $this->name = $parent->getName();
          $this->email = $parent->getEmail();
     }

 public function someFunction()
 {
       //some code here
 }
}

Of course the getName() and getEmail() would be made. Is this the best way to do it? Thanks

[banzaimonkey]

Then it seems to a be an issue of flow. You shouldn't have, afaik, a loop-back in inheritance (because this has the risk of infinite recursion). You'd need to do your validation before creating the object in the first place. So you might have something like this:

<?php

function validation($input1, $input2)
{
  if ($input1 == validusername && $input2 == validpassword)
  {
    return true;
  }

  else
  {
    return false;
  }
}

if (validation($username, $password) === true)
{
  $user = new Parent();
}

...

class Parent
{
  //blah blah blah
}

Regarding your second question...

$this->name = $parent->getName();
$this->email = $parent->getEmail();

If you have the name and email set as variables in the parent class, you shouldn't need to use functions to access them from the child. You'd only need to use the functions to access the data from the parent's parent class.

I.e.

Class1
  Class2 extends Class1
    Class3 extends Class2

Class3 should already have inherited Class2's variables. If you're in Class1 and want Class2's variable, then you need to access it via a function.

[Shrike]

You can mark the properties in Parent as protected to make them available in Child through inheritance. private properties will only ever be available in the class in which theyre defined.

[ahundiak]

Of course the getName() and getEmail() would be made. Is this the best way to do it? Thanks

This is probably the best way to go about it.

However, as banzaimonkey implied, having to change an object into a different class is typically not an ideal design. And of course you need to use protected keywords as Shrike said. Might want to review the PHP5 object section in the manual.

[Banacek]

Right, they should be protected. Sorry about that. I understand that a class shouldn't be created before the validation occurs, but if I wanted to include all the functions in a class file, wouldn't they need to be associated with at least the parent? You shouldn't have "loose" functions, right? That's why I was creating the parent before then figuring out which child the object should be. Thanks for the help, btw.

[ahundiak]

What sort of functions are you talking about? Perhaps you could use a static method

$object = Parent::validateAndConstructObject();

and have it determine and return the correct class?

[Banacek]

ahundiak wrote:

What sort of functions are you talking about? Perhaps you could use a static method

$object = Parent::validateAndConstructObject();

and have it determine and return the correct class?

That sounds like a good idea. Thanks!