Acessing object from object [duplicate] - php

Question

This question already has answers here:
Use global variables in a class
(4 answers)
Closed 10 years ago.
I'm starting with OOP in PHP and there is something I'd like to do. Let me show an example:
classes.php
<?php
class a {
public function a() {
echo 'a';
}
}
class b {
public function calla() {
$x->a();
}
}
?>
index.php
<?php
include('classes.php');
$x = new a();
$d = new b();
$d->calla();
?>
Is this possible? I know I can do something like:
class b {
public function calla($object) {
$object->a();
}
}
and
$d->calla($x);
but is the first example possible to do?

Answer 1

So you want to use $x as global variable? Syntax is the same, object or not:
class b {
public function calla() {
$GLOBALS['x']->a();
}
}
... or:
class b {
public function calla() {
global $x;
$x->a();
}
}
Of course, it's a horrible design that injects hard to track dependencies and will probably lead to unexpected side effects and head-scratching.
Additionally, a() is a poor method name for class a because it's the PHP 4 syntax for constructors. If you run this code:
<?php
class a {
public function a() {
echo 'a';
}
}
class b {
public function calla() {
$GLOBALS['x']->a();
}
}
$x = new a();
$d = new b();
$d->calla();
... you'll see that a() runs twice. Guess why?

Answer 2

I think I understand what you're trying to ask but you're mixing up parameters visibility concept with object passing in class methods. So let's clean up...
In your classes.php file the method calla() of the class b as absolutely nothing to do with class a, unless $x itself is an instance of the class a.
In your index.php file you instantiate $x as class a, but it is a global variable, and the class b has no visibility on it. Moreover, your call to $d->calla() would return an error because you are accessing a private method from outside.
Your third example gets closer to the solution, passing the instance to the calla() method helps class b seing the instance of class a, I guess you want to edit your index.php file to:
<?php
include('class.php');
$x = new a();
$d = new b();
$d->calla($x);
?>
But this still won't work until you change the private methods to public ones.