About the (Safak Ozpinar / safakozpinar at gmail)'s great note, you can still have the same behavior than inheritance using trait with this approach :
<?php
trait TestTrait {
public static $_bar;
}
class FooBar {
use TestTrait;
}
class Foo1 extends FooBar {
}
class Foo2 extends FooBar {
}
Foo1::$_bar = 'Hello';
Foo2::$_bar = 'World';
echo Foo1::$_bar . ' ' . Foo2::$_bar; // Prints: World World