scope of class properties in php

Question

I have a class which is instantiated globally and in turn instantiates a second class from within its constructor. What I can't figure out is how to gain access to properties of the first class from the second.

 <?php

    class Foo 
    { 
       public $bar;
       public $myProperty;
       public function __construct() 
       {
           $this->bar = new Bar();
           $this->myProperty='hello';
       }
    }

    class Bar 
    { 
       public function __construct() 
       {
           echo $foo->myProperty; //I can't see that from here
       }
    }

    $foo = new Foo(); 

   ?>

what might be the correct way of going about this?

Ahmed Siouani · Accepted Answer · 2013-12-31 14:11:08Z

3

You problem has nothing to do with scope of class properties, it's with scope of ordinary variables. $foo is a global variable, so it's not normally visible inside functions. You need to do:

public function __construct() 
{
    global $foo;
    echo $foo->myProperty;
}

However using global variables is usually bad form. It would be better if you passed $foo as a parameter to the Bar constructor.

edited Dec 31, 2013 at 14:11

Ahmed Siouani

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answered Dec 31, 2013 at 12:41

Barmar

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7 Comments

Barmar Over a year ago

It looks like you have an infinite regress. The Foo constructor creates Bar, and the Bar constructor tries to access the properties of $foo. But $foo won't have a value until the Foo constructor returns.

user2727841 Over a year ago

you use gobal keyword but its also won't work. What if I use $this instead of $foo???

Barmar Over a year ago

Nothing will work. You're trying to access something before it's finished constructing.

andrew Over a year ago

agreed with @user2727841, use of global does not work, but I can pass itself into the constructor $this->bar = new Bar($this); I do prefer that. +1

Barmar Over a year ago

But you won't be able to access $foo->myProperty, because the constructor doesn't assign that until after it call new Bar($this).

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