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Another OOP beginner question

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Jan 18.2009

Hi,

I’m having some trouble with php inheritance and constuctors and I would like to know the right way this is done so I can debug the code more easily.

If the parent class has a set of properties (a,b,c) that are given values in the constructor and a child class adds a few more properties (d,e,f) that are given values in its constructor, how do i call the child class? I can think of many ways to do this but none seems correct(or works). What values do i pass to the child class?

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PHP

5 Comments(s) ↴

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@CoutJan 18.2009 — You can always just from parents to children inherit methods and variables.

Example:
[code=php]<?php

class parentClass
{
public $a = null;

public function __construct()
{
$this -> a = "Add_A";
}
}

class childClass extends parentClass
{
public $b = null;

public function __construct()
{
parentClass::__construct();
$this -> b = "Add_B";
}
}

$parent = new parentClass();
// exists in class parentClass
echo "<br/>parent a : " . $parent -> a;
// does not exists in class parentClass
echo "<br/>parent b : " . $parent -> b;
// delete object
unset( $parent );

$child = new childClass();
// exists in class parentClass and childClass
echo "<br/>child a : " . $child -> a;
echo "<br/>child b : " . $child -> b;
// delete object
unset( $child );
?>[/code]
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@RoxyBooauthorJan 18.2009 — What I was talking about is this:

<?php

class parentClass
{
public $a = null;

public function __construct($a)
{
$this -> a = $a;
}
}

class childClass extends parentClass
{
public $b = null;

public function __construct($a,$b)
{
parentClass::__construct($a);
$this -> b =$b;
}
}

$parent = new parentClass('Add_a');
// exists in class parentClass
echo "<br/>parent a : " . $parent -> a;
// does not exists in class parentClass
echo "<br/>parent b : " . $parent -> b;
// delete object
unset( $parent );

$child = new childClass('Add_a', 'Add_b');
// exists in class parentClass and childClass
echo "<br/>child a : " . $child -> a;
echo "<br/>child b : " . $child -> b;
// delete object
unset( $child );
?>

Now it works OK in php4 (I didn't know of :: ). I have to repeat 'Add_a' twice though (once to the parebt and once to the kid).

You can pass variables to the constructor in php5, can't you?

I was so sure I had picked a good webhost...
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@CoutJan 18.2009 — Year, in php5 I can pass vars to the constructor. And please use the BB Code "php" for the code. Do you pay for your webhost?
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@RoxyBooauthorJan 18.2009 — I pay alright,

And it's even more on the expensive side.
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@NogDogJan 18.2009 — Note that there is no [b]__construct()[/b] "magic method" in PHP4. You instead have to use a method with the same name as the class as the constructor. (PHP5 supports this, too, if you use it [i]instead[/i] of the __construct() method.)

But you really want to move to PHP5 if at all possible in order to take advantage of the much-enhanced OOP support it provides over PHP4.
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