Instanciating Objects

PHPGuru2

I just found out that it's not possible to instanciate two or more same object in one page.

// These cannot be done in the same page.
$one = new A();
$two = new A();

Is there a way to work around with this???

PHPGuru2

I had a class that instanciates other class within its constructor (a class instanciates database class within it as its property) and also had another class that instanciates same database class. I was getting an error that you cannot instanciates a same class twice in the same page (don't know why PHP won't let you do that... Maybe because of its current restriction??)

The only way to work around with this is to pass a database class by reference.

class A()
{
function A(&$database_object)
{
$this->db = &$database_object;
.....
.....
}
}

class B()
{
function B(&$database_object)
{
$this->db = &$database_object;
.....
.....
}
}

Let me know if someone else has better idea or way to do it.

Tristan_Wells

You can use extends to make an identical class.

<?php
class class1
 {
   var $varible = 'hiya';
   function class1()
    {
      echo($this->varible);
    }
 }
class class2 extends class1
 {
 }
$class1 = new class1();
$class2 = new class2();
?>

shareaweb

If my memory serves me right I believe you can also instantiate the classes by reference, but this is best only at design time and not at run-time, and only best in php 4.3 or above.

$class1 =& new classa;
$class2 =& new classb;

See the implications of this at the zend.com webcast site under PHP5 intro.. the one where Zeev expands on the problems of objects in php4

But the usual is like so:

<?
// this is mine...
$his = new Automobile;
$his->make = "Ferrari";
$his->colour = "Black";
$his->shape = "Cigar";

// ...and this is yours
$hers = new Automobile;
$hers->make = "Porsche";
$hers->colour = "Silver";
$hers->shape = "Torpedo";

// hey...i can dream, can't i

// i feel like taking mine out for a spin
$his->start();

// speed limit? you must be joking!
$his->accelerate(180);

// joining me, are you?
$hers->start();
$hers->accelerate(150);

// oops...was that a speed trap?
$his->decelerate(80);
$hers->decelerate(80);

// busted!
$his->stop();
$hers->stop();

Check your parenthesis on instantiating!

-E-

ahundiak

$a = new A();
$b = new A();

Is perfectly legal and will work. Of course you get two different objects. Better recheck your code.

PHPGuru2

Found out that if a class has require_once() or include_once() within the constructor, then you cannot instanciate that class more than twice in the same page.

class A
{
     function A()
     {
          require_once('blah.php');
          .....
          .....
     }
}

$one = new A(); // This works.
$two = new A(); // This is where you get an error message.

Drakla

Guru, you absolutely sure about the require thing? I've just tested this and it works absolutely fine:

class doesnowt
{
	var $x;

function doesnowt()
{   echo "require result:".require_once("..//mysql//mysqlclassinc.php");
	echo "<br>I do absolutely nowt<br>";
}
}

$a=new doesnowt;
$b=new doesnowt;

printing
require result:1
I do absolutely nowt
require result:1
I do absolutely nowt

Can you shove your class code in to see if there's something you've gone code-blind to. That happens to me all the time.

PHPGuru2

My class is too much to write in here, but this is how it goes.

I have a configuration file that has an array that holds about 15 different values in its elements.

$config['blah'] = "blah";
$config['blah2'] = "blah2";
....
....

My class requires this file to initialize its property when it is instanciated.

class A
{

 var $property;

 function A()
 {
      require('config.inc.php');
      if(isset($config) && is_array($config))
      {
           ..... // initialization here
      }
      else
      {
           echo("Fatal Error: Object cannot be instanciated.");
           exit();
      }
 }

}

For some reasons when the second class is instanciated, and if I have the require_once() instead of the require(), if statement that checks $config doesn't return true, therefore it prints out the "fatal error" comment and it exits the script. (This goes to the same for include_once() and include().)

Maybe this is a bug that PHP has or that's how class definition and instanciation is processed in PHP?? I have no idea.

Drakla

Riiight, I think I understand what's going on there.

The scope of the variables and things that you get with the require_once() only exist within that function... when you create an object of that class the first time, the include happens - all the functions and variables in the script are there to grab...

The second time you do it the require_once() doesn't run at all, so your class is seeing nothing from that external script. So basically it's a scoping problem. That's why using require() and include() which grab the data every time works.

Phwew! I was bricking it for a second there.

PHPGuru2

Yeah that sounds right and makes sense.