Factory Pattern and Singleton

[Craige]

How would you recomend I use factory method to create a Singleton object? With the singleton pattern you have a static instalizer function and a private construct. This does not exactly work in my favor. I am not sure how, or if it is even possible, to go about this. Andybody else know?

[rvdavid]

PHP Code:

function getSingleton()
{
    return Singleton::getInstance();
} 


This is done to avoid peppering your code with static calls. Factory methods keep the assembly abstracted. So it gives you the flexibility to refactor later on, like when you decide an object isn't going to be a singleton anymore

Regardds,

[Craige]

Originally Posted by rvdavid

PHP Code:

function getSingleton()
{
    return Singleton::getInstance();
} 


This is done to avoid peppering your code with static calls. Factory methods keep the assembly abstracted. So it gives you the flexibility to refactor later on, like when you decide an object isn't going to be a singleton anymore

Regardds,

Well thank you, but I am not sure that helped me at all. That really did not answer my question about how to instalize a singleton pattern class throgh a foctory method call.

[ironikart]

Well thank you, but I am not sure that helped me at all. That really did not answer my question about how to instalize a singleton pattern class throgh a foctory method call.

rvdavid's example is exactly what you are asking. Singleton::getInstance() returns an instance of the singleton, which is returned via the factory method. If you use:

$singleton = $myclass->getSingleton()

Then you have effectively called Singleton::getInstance();

[rvdavid]

Hi,

Originally Posted by Craige

Well thank you, but I am not sure that helped me at all. That really did not answer my question about how to instalize a singleton pattern class throgh a foctory method call.

You've probably phrased the question incorrectly somehow. Or we've not understood it correctly. I know what it's like so don't worry about it.

Let's start with the subject matter - What exactly are you trying to achieve?

Maybe you are looking for other ways to implement the Singleton pattern in PHP?

If so, what's wrong with having a static instance variable, private constructor and static instance accessor method?

PHP Code:

class Singleton 
{
    private static $instance = false;

    private __construct()
    {

    }

    public static function getInstance()
    {
          if (!self::$instance) {
             self::$instance = new Singleton();
          }
          return self::$instance;
    }
} 


What is it about this implementation that does not work in your favour?



regards,

[Craige]

Originally Posted by rvdavid

Hi,

You've probably phrased the question incorrectly somehow. Or we've not understood it correctly. I know what it's like so don't worry about it.

Yeah, I probably phrased it wrong

Let's start with the subject matter - What exactly are you trying to achieve?

Instalize a singleton class, through a factory mathod class. However, the singleton class is mixed among an assortment of other classes aswell in the factory method

Maybe you are looking for other ways to implement the Singleton pattern in PHP?

If so, what's wrong with having a static instance variable, private constructor and static instance accessor method?


What is it about this implementation that does not work in your favour?

regards,

Nope That isn't it.

I ended up working out a rather simple way to get this done. Here is the code (untested), do you see what I was trying to do now?

PHP Code:

public static function loadModules( /* List of modules to be loaded */ )  {
    $argNum = func_num_args();
    $argVal = func_get_args();


    for ( $i = 0; $i <= $argNum; ++$i )  {

      // If the paramater has a s_ starting it, the class is a singleton, and special care is needed.
      if ( ($tmp = strpos($argVal[$i], 's_') ) )  {
        $argVal[$i] = substr($tmp, 2);
        $singleton = true;
      }

      $file = $modulePath . $argVal[$i] . '.mod.php';

      if ( file_exists($file) )  {
        if ( @include_once $file )  {

          if ( $singleton == true )  {
            $this->registry[$argVal[$i]] = $argVal[$i]::instalize();
            $singleton = false; // reset singleton variable
          }
          else  {
            $this->registry[$argVal[$i]] = new $argVal[$i]();
          }

        }
      }
      else
        throw new exception('Module file \'' . $file . '\' not found', 1.2);


    } // End For Loop

    return true;
  } 


[rvdavid]

ahh a dynamic loader/container huh?
I understand now

One thing though, why are you putting a singleton in the registry?

couldn't you just do a check if it exists in the registry?
If it exists return the instance from the registry
if not, it creates an instance assigns it to the registry and returns the instance from the registry.

What are your thoughts on this?

regards,

[ironikart]

Yeah, there's no point putting a singleton in the registry - defeat's the purpose. Your registry should handle loading single instances.