Avoiding if-statements with object oriented design, PHP - php

Question

I'm basically creating a display-module for an ad-system I've created.
I'm trying to avoid the following construction, with repeated if-statements.
My gut feeling tells me there's a smarter way to do this, maybe with polymorphism?
<?php
class Ad {
public $adState = 'active';
}
class AdWriter {
public function displayAd(Ad $ad, $viewmode = 'visitor') {
if ($viewmode =='visitor') {
if ($adState == 'active') {}
else if ($adState == 'paused') {}
else if ($adState == 'inactive') {}
}
else if ($viewmode = 'owner') {
if ($adState == 'active') {}
else if ($adState == 'paused') {}
else if ($adState == 'inactive') {}
}
else if ($viewmode == 'administrator') {
if ($adState == 'active') {}
else if ($adState == 'paused') {}
else if ($adState == 'inactive') {}
}
}
}
?>

Answer 1

Apply the Refactoring Replace Conditional with Polymorphism and have a look at the State Pattern.

Answer 2

You could create an Factory (Pattern), using an switch on viewmode and create an specific Ad implementing an interface having an simple function 'display' for example.
Pseudo example:
class AdFactory {
public static function getAd($sType) {
switch($sType) {
case "AdOne":
return new AdOne();
case "AdTwo":
return new AdTwo();
}
}
throw new Exception("Unknown ad!");
}
class AdOne implement AdInterface {
public function display() {
// All that AdOne does when displaying.
}
}
interface AdInterface {
public function display() { }
}
$oAd1 = AdFactory::getAd('typeOne');
$oAd1->display();
$oAd2 = AdFactory::getAd('typeTwo');
$oAd2->display();

Answer 3

Instead of passing $viewmode, pass an object that would encapsulate the logic for this viewmore and call its method that would do the work. This way you'll avoid the need for if-statements.

Answer 4

I'm sneaking onto StackOverflow at work, so don't have time to write a detailed reply of all your possibilities.
But to 'tidy up' those ifs, you can do this:
switch $viewmode {
case 'visitor':
your_code_here;
break;
case 'owner':
your_code_here;
break;
default:
will_run_if_nothing_above_matches;
break;
}

Answer 5

switch($viewmode){
case "visitor":
switch($adstate){
case "active":
//statement
break;
case "paused":
break;
case "inactive":
break;
}
break;
case "owner":
break;
case "administrator":
break;
}

Answer 6

In 8 chapter of this book you can find very detailed answer to your question.
In short: use Composition or Factories. (see answer of Wesley van Opdorp).
Also, avoid using string arguments as enumerable:
$viewmode = 'visitor'
with this argument, you will have to keep in memory all possible values of this argument. Or look into code of function to remember them. And these values are strings - good place for typos. Also, it will be very difficult to change values in feature, because all calls of this method will contain hardcoded strings.
Use class-constants:
class AdWriter {
const view_mode_visitor = 1;
...
Also, $adState - wrong code, should be $ad->state. But using public fields it's bad practice too :)