// Only from inside the same class $this->processSomething([__CLASS__, 'myStaticCallback']); // From either inside or outside the same class $myObject->processSomething(['\Namespace\MyClass', 'myStaticCallback']); $myObject->processSomething(['\Namespace\MyClass::myStaticCallback']); // PHP 5.2.3+ $myObject->processSomething([MyClass::class, 'myStaticCallback']); // PHP 5.5.0+