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I have a reoccuring problem that I am currently tackling like so -

a POST variable coming in to the script which has a platform, the platform is from a list such as: xbox,ps3,pc,mobileapp,mobilegame etc

for each different platform I want to be able to do something different in my script but in some cases I want code to do very similar things at the moment I do something like this:

$platformArray = array(
   'ps3'=>array('displayName'=>'playstation 3','function'=>'funcPS3'),
   'xbox'=>array('displayName'=>'Xbox','function'=>'funcXbox')
)
//similar amongst all platforms code on line below
echo 'you have a :'.$platformArray[$_POST['platform']]['displayName'].' for playing       games';

call_user_func($platformArray[$_POST['platform']['function']);

function funcPS3(){
   echo 'ps3 specific code'; 
}

 function funcXbox(){
   echo 'xbox specific code';
 }

I want to move towards a OOP approach in my code, I want to use objects as my data storage medium rather than arrays as I'm doing now, but I do sometimes need to define attributes in the code ahead of time, how could I do the above but with objects?

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  • 2
    have you looked into how objects work? What have you tried? Commented Feb 27, 2013 at 21:24
  • yeah on a basic level I understand they generally have private internal variables which you can set and get with functions, I want to set some ahead of time I suppose I could load multiple instances of objects up with the variables, I guess I could refer to the object using ${$_POST['platform']} can I do things like ${$_POST['platform']}->myclassfunc(); ? apologies for not trying it out I've not got my setup here Commented Feb 27, 2013 at 21:29
  • I'd make a base "platform" class with the similar parts predefined, then make XBOX/PS3/PC classes that inherit it and overload some of the functions with platform-specific actions. Commented Feb 27, 2013 at 21:33
  • @GigaWatt and you'd need a factory that knows about all types of subclasses to know which one to instantiate, I don't think subclasses is the answer here, see my answer... coming up Commented Feb 27, 2013 at 21:34
  • 1
    You need to do a lot more reading on classes and classes in PHP. You need to design your own class, declare a new object and then call your functions on that object to do whatever. Commented Feb 27, 2013 at 21:34

3 Answers 3

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4

I would recommend for you to start by understanding polymorphism. This lecture should be good start.

When you are trying to create behavior, based on some flag, you should implement two classes with same interface:

class Xbox
{
    private $displayName = 'XBox 360';

    public function identify()
    {
        // Xbox-specific stuff
        return  ':::::::::::'. $this->displayName;
    }
}

class PS3
{

    private $displayName = 'Playstation 3';

    public function identify()
    {
        // playstation-specific stuff
        return '+++'. $this->displayName . '+++';
    }
}

The two classes have method with same name that would do different things;

$platform = $_POST['platform'];
// classes in PHP are case-insensitive
// expected values would be:  xbox, Xbox, ps3, pS3
if ( !class_exists($platform) )
{
     echo "Platform '{$platform}' is not supported";
     exit; 
     // since continuing at this point would cause a fatal error, 
     // better to simply exit
}

$object = new $platform;
echo $object->identify();

Basically, in this case you really do not care, which type of platform you are working with. All you need to know is that they both have same public interface. This is called "polymorphic behavior".

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3 Comments

POST Parameter mapping to classes is a bad vulnerability. Which is why you need a registry of allowed parameters instead of just letting the user instantiate any class in the system. This was my initial idea as I was answering, but I didn't want to suggest a vulnerable way.
@JuanMendes , Actually that "vulnerability" can be handled by simple routing mechanism. And restricting classes to a specific namespace. Answer in SO are never to be taken as "production read code". The OP was asking to understand OOP, so, instead of giving a good object oriented example (but one with obvious and easily avoidable flaw), you opted for an example which advocated a procedural code, that abuses global state.
I agree, I also did not want to take the time to work out the answer to its fullest. But since your comment, decided to improve the answer to avoid people like you assuming that I don't know OOP :). Can't possibly teach OOP in one post like this, but I hope the steps I posted in my updated answer are helpful to the OP since they gradually move from a naive explanation to a nice one (based on your idea, plus an explicit interface) and explain why. I loved the youtube.com/watch?v=-FRm3VPhseI link. I'm a big believer in dependency injection and avoiding global state.
0

I'm going to work from a very naive OO version, to what is considered "good" OO code, using polymorphic behavior and avoiding global state.

1. Not polymorphic and has global static data

This is pretty bad because it is really just a wrapper object over procedural code. It needs a map of functions to call for each type of platform.

class Platform {    
    private static $platformArray = array(
       'ps3' => array(
           'displayName'=>'playstation 3',
           'function'=>'funcPS3'
        ),
       'xbox' => array(
           'displayName'=>'Xbox',
           'function'=>'funcXbox'
       )
    );

    private $type;

    public function __construct($type) {
        if (!array_key_exists($type, self::$platformArray)) {
             throw new Exception("Invalid Platform type $type" );
        }
        $this->type = $type;
    } 

    public function printCode() {
        // This was a question embedded within your question, you can use 
        // http://php.net/manual/en/function.call-user-func.php
        // and pass an instance with a method name.     
        return call_user_func( array($this, self::$platformArray[$this->type]) );
    }

    private function funcPS3(){
        echo 'ps3 specific code'; 
    }

    private function funcXbox(){
        echo 'xbox specific code';
    }    
}

$plat = new Platform($_POST['platform']);
$plat->printCode();

2. Polymorphic... but it still uses global data

By creating a base class you can implement behavior in subclasses, creating separate class for each concern. The big problem here is that subclasses need to register with a global registry.

abstract class Platform {
    abstract protected function getCode();
    public function printCode() {
        echo $this->getCode();
    }

    private function __construct() {} // so only factory can instantiate it
    private static $platformArray = array();

    public static function create($type) {
        if (!array_key_exists($type, self::$platformArray)) {
             throw new Exception("Invalid Platform type $type" );
        }
        return new self::$platformArray[$type];

    }         

    public static function addPlatform($type, $ctor) {
        if (!is_subclass_of($ctor, 'Platform')) {
             throw new Exception("Invalid Constructor for Platform $ctor" );   
        }
        self::$platformArray[$type] = $ctor;
    }
}

class PlatformXBox extends Platform{
     protected function getCode() {
         return 'xbox specific code';
     }
}
Platform::addPlatform('xbox', 'PlatformXBox');

class PlatformPs3 extends Platform {
     protected function getCode() {
         return 'ps3 specific code';
     }
}
Platform::addPlatform('ps3', 'PlatformPs3');

$plat = Platform::create($_POST['platform']);
$plat->printCode();

3. Polymorphic, no global data

By putting your code into a namespace, you avoid the static code in the base class and avoid the dangers of mapping post parameters directly into classes. 

namespace platform {

interface IPlatform {
   public function getDisplayName();
   public function getCode();
}

class PlatformFactory {
    static public function create($platformType) {           
        $className = "\\platform\\$platformType";
        if ( !is_subclass_of($className, "\\platform\\IPlatform") ){
            return null;
        }
        return new $className;
    }
}

class Xbox implements IPlatform {
    public function getDisplayName(){
        return 'xbox';
    }
    public function getCode(){
       return 'xbox code';   
    }
}

class Ps3 implements IPlatform {
    public function getDisplayName(){
        return 'ps3';
    }
    public function getCode(){
        return 'ps3 code';   
    }
}

}

Now you can use those classes like the following

$platform = platform\PlatformFactory::create('xbox');
echo $platform->getCode() ."\n" ;

$platform2 = platform\PlatformFactory::create('ps3');
echo $platform2->getDisplayName()."\n";

$noPlatform = platform\PlatformFactory::create('dontexist');
if ($noPlatform) {
    echo "This is bad, plaftorm 'dontexist' shouldn't have been created";
} else {
    echo "Platform 'dontexist' doesn't exist";
}
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2 Comments

@tereško I did explain the problems with this approach. Essentially, you need a mapping from post parameters to different types of classes which you achieved by making your code vulnerable.
@tereško Took your advice and improved the answer, please let me know of any remaining problems with the suggested solution
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You might want to create a class called platforms and within the class a different method for each platform:

class platforms {
   //Create your variables here, also called properties.
   public $displayName;

   //Create a function, also called a method for each platform you intent to use.
   public function xboxPlatform(){
        //Code comes here what you want to do.
   }
}

Hope this helps.

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3 Comments

This doesn't really address the question. How will you call the method based on a POST variable?
I have a fully functional tutorial using OOP and PDO for you if you want to take a look at that: [link]docs.google.com/file/d/0B0fx_EGx3tG_SGFwcmZDMlJQbFE/…
True answer 1 is the better option.

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