How to set property in parent class and use it in child class?

Question

I would expect the following code to write "bar", but getFoo returns NULL.

What is the problem with that code, and how can i fix this?

<?php class A { protected $foo; public function getFoo() {return $this->foo;} public function setFoo($foo) {$this->foo = $foo;} } class B extends A{} $a = new A(); $a->setFoo("bar"); $b = new B(); echo $b->getFoo();

OOP concept fails here. The object $a sets the variable $foo='bar' but the object $b hasn't set the variable $foo yet. So it returns null. Whereas $a->getFoo() would return "bar" not null. — Rohit Subedi
– Rohit Subedi, Commented Mar 7, 2014 at 10:31

Jesper Blaase · Accepted Answer · 2014-03-07 10:30:14Z

Im not really sure what you are doing, and i am quite sure you should read up on exactly how inheritance and objects work. You are specifying 2 classes witch is a template to build an object from. You the instanciate 2 objects $a and $b but these two objects do not share data.

You could use a static variable to do what you want but im not really sure what you are trying to achieve:

<?php class A { protected static $foo; public function getFoo() {return self::$foo;} public function setFoo($foo) {self::$foo = $foo;} } class B extends A{} $a = new A(); $a->setFoo("bar"); $b = new B(); echo $b->getFoo();

Outputs: "bar"

marekful · Accepted Answer · 2014-03-07 10:28:54Z

Your expectation is wrong. $a and $b are different instances. You set $foo in one instance, then create another that does not know about the first one.

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