Trying to implement proper patterns in PHP, is this right?

The below code is something I just wrote up after reading a bit about design patterns and I want to know if I have the gist of it. This is supposed to implement a Mediator design pattern, as well as using interfaces over implementation and the Factory design pattern.

<?php
interface iNav_Walker
{
    public function walk();
}

class Nav_Walker
{
    public static function factory()
    {
        $class_name = 'Generic_Nav_Walker';
        $class_name = filter( 'nav_walker_class', $class_name ); 

        $object = new $class_name;

        return $object;
    }

    private function __construct()
    {
        return FALSE;       
    }
}

class Generic_Nav_Walker implements iNav_Walker
{
    public function walk() 
    {
        echo 'Generic Nav Walker';
    }
}

class Custom_Nav_Walker implements iNav_Walker
{
    public function walk() 
    {
        echo 'Custom Nav Walker';
    }
}

class MyPlugin 
{
    public static function use_custom_walker( $walker_class )
    {
        return 'Custom_Nav_Walke开发者_运维问答r';
    }
}

add_filter( 'nav_walker_class', array( 'MyPlugin', 'use_custom_walker_class' ) );

$nav_walker = Nav_Walker::factory();
$nav_walker->walk();

The obvious benefit of this approach is making it easy to replace an applications default class with a custom one. Your custom one could even extend the original class and just override a single method could it not? Like this:

<?php
class Generic_Nav_Walker implements iNav_Walker
{
    public function walk() 
    {
        echo 'Generic Nav Walker';
    }

    public function other_func()
    {
        // Do something
    }

    public function other_func2()
    {
        // Do something
    }
}

class Custom_Nav_Walker extends Generic_Nav_Walker implements iNav_Walker
{
    public function walk() 
    {
        echo 'Custom Nav Walker';
    }
}

Because you may only wish to change some small part of the class, or is this bad practice?

---

Trying to implement proper patterns in PHP, is this right?

No, no need to look at your code to realise you don't understand what patterns are.

A pattern is what your code is - not what it should be or any sort of template. It is a quick way of describing the abstract functionality of module. And therefore a useful tool for describing code and for planning a curriculum around.

Planning and implementing your project as a set of patterns is a very misguided approach to software engineering / deveopment.