Is it bad practice to declare a class's ctor 'final' in PHP?

Question

If I have a parent class that is extended by lots and lots of other classes, and I want to make sure the parent class's constructor is ALWAYS run, is it a bad idea to declare the constructor final?

I was thinking of doing something like this:

class ParentClass {

    public final function __construct() {

        //parent class initialization...

        $this->construct();

    }

    protected function init() {

        echo 'constructing<br>';

    }

}

class ChildClass extends ParentClass {

    protected function init() {

        //child class initialization

        echo 'constructing child<br>';

    }

}

that way the child class can have a sort-of constructor, and the parent class's constructor will always execute. Is this bad practice?

Answer 1

After finalizing the constructor, you can't pass any variables to initializing function. It forces users of you class to use globals as settings for their child classes.

In Zend Framework using overridable init() is common practice, but I've never seen finalizing a constructor there.

Answer 2

Declaring a final __construct ensures that no one who extends your class can implement a method with the same name. On the surface of it, this would seem like it would mean no one else can declare a constructor for sub-classes of this class, but this is not true, since the PHP 4 style of ClassName() still works just fine as an alternate name for the constructor. So really, declaring a constructor as final gets you nothing in PHP.