Removing repeated conditions using polymorphism and the Factory pattern - php

Question

<?php
/**
* My codebase is littered with the same conditionals over and over
* again. I'm trying to refactor using inheritance and the Factory
* pattern and I've had some success but I'm now stuck.
*
* I'm stuck because I want to derive a new class from the one
* returned by the Factory. But I can't do that, so I'm obviously
* doing something wrong somewhere else.
*/
/**
* The old implementation was as follows. There's if statements
* everywhere throughout both LayoutView and ItemIndexView and
* SomeOtherView.
*/
class LayoutView { }
class IndexView extends LayoutView { }
class SomeOtherView extends LayoutView { }
/**
* Below is the new implementation. So far I've managed to tidy
* up LayoutView (I think I have anyway). But now I'm stuck because
* the way I've tidied it up has left me not knowing how to extend
* it.
*
* For example's sake, let's say the conditions were relating to a
* type of fish: salmon or tuna.
*/
abstract class LayoutView {
protected function prepareHeader() { echo __METHOD__, "\n"; }
protected function prepareLeftHandSide() { echo __METHOD__, "\n"; }
protected function prepareFooter() { echo __METHOD__, "\n"; }
public function prepare() {
$this->prepareHeader();
$this->prepareLeftHandSide();
$this->prepareFooter();
}
}
class SalmonLayoutView extends LayoutView
{
protected function prepareLeftHandSide() { echo __METHOD__, "\n"; }
}
class TunaLayoutView extends LayoutView
{
protected function prepareLeftHandSide() { echo __METHOD__, "\n"; }
protected function prepareFooter() { echo __METHOD__, "\n"; }
}
class ViewFactory {
public static function getLayoutView($fishType) {
switch($this->$fishType) {
case 'salmon':
return new SalmonLayoutView();
break;
case 'tuna':
return new TunaLayoutView();
break;
}
}
}
/**
* Now LayoutView has been cleaned up and the condition that was once
* scattered through every LayoutView method is now in one place.
*/
$view = ViewFactory::getLayoutView( Config::getOption('fishtype') );
$view->prepare();
/**
* Now here's where I'm stuck. I want to effectively extend whatever
* class $view is an instance of.
*
* The reason being, I wish to derive a view to show an index of
* articles within the appropriate *LayoutView. The IndexView code is
* the same for Salmon and Tuna.
*
* I can do something like this:
*/
class SalmonIndexView extends SalmonLayoutView { }
class TunaIndexView extends TunaLayoutView { }
/**
* But then I'll be writing the same IndexView code twice. What I'd
* like to do is something like this:
*/
$view = ViewFactory::getLayoutView( Config::getOption('fishtype') );
class IndexView extends get_class($view) { }
/**
* But I'm pretty certain that's not possible, and even if it was
* it seems very wrong.
*
* Can someone more experienced in refactoring and OO please let
* me know where I've gone wrong and suggest a clean way to solve
* this?
*/

Answer 1

If the IndexView code really is the same then you don't need inheritance, but composition. Add, in your base LayoutView class, an instance of IndexView that then you'll be able to call from each *LayoutView.
Inheritance is due only when the relationship between objects is is-a. I deduce that an IndexView is not a LayoutView, but rather the LayoutView has an IndexView.
Check this out, I don't agree with everything it says, but still:
http://phpimpact.wordpress.com/2008/09/04/favour-object-composition-over-class-inheritance/

Answer 2

Just pass the template as a parameter to the subviews you'll compose. I don't think that'd be evil in this case. Although if it's a standard framework you might be better asking in their forums, because they might have a functionality we are unaware of for this case (it usually happens)
You could have something like
class LayoutView {
protected View $subview; //Potentially an array of views
public function prepare() {
// empty, to be filled out by derived classes
}
public function setSubView($view) { $this->subview = $view; }
public function display() {
$this->prepare();
$this->subview->prepare($this->template);
$this->template->render();
}
}
class IndexView {
protected View $subview; //Potentially an array of views
public function prepare() {
// empty, to be filled out by derived classes
}
public function prepare($template) {
//operate on it, maybe even assigning it to $this->template
}
public function setSubView($view) { $this->subview = $view; }
public function display() {
$this->prepare();
$this->subview->prepare($this->template);
$this->template->render();
}
}