Question

When you extend a class, the child inherits the properties by copy pasting those (new variables, same values), therefore consuming more memory, or… references them?

Hope I’ve made myself clear.

Answer 1

I’m going to assume you’re referring to zvals, rather than common variable referencing. In that case, yes, it does appear that the inherited property is just an internal reference up until the point you change the value in your extended object. For more info, see the manual: http://www.php.net/manual/en/features.gc.refcounting-basics.php

An example:

class test
{
    public $a = 'asdf';
    
}
class test2 extends test
{
    
}
class test3 extends test
{
    
}   
class test4 extends test
{
    
}   

$test2 = new test2;
debug_zval_dump($test2);
$test2->a = 1;
debug_zval_dump($test2);

Results:

object(test2)#1 (1) refcount(2){
  ["a"]=>
  string(4) "asdf" refcount(5)
}
object(test2)#1 (1) refcount(2){
  ["a"]=>
  long(1) refcount(1)
}