How would you do it (singletons)?

[Adam]

Turning the 'OOP conventions' topics into a trilogy I guess, how would you (or what's your preferred method to) implement a singleton design pattern? Mainly interested in how you'd reference the class file and name. A Zend style approach or perhaps something  a little more bespoke?

[ignace]

I would avoid it.

 

http://code.google.com/p/google-singleton-detector/wiki/WhySingletonsAreControversial

[Adam]

I see. Is this a shared opinion? My knowledge in this area is quite limited to be fair, which why I asked really.

---

 

Allow me to re-phrase the question, how would you go about object instantiation?

[Daniel0]

My favorite way of handling the singleton pattern is by avoiding it.

[Adam]

Yeahh fuck, was way off with this topic. Let's ignore it 'eh!

[ignace]

how would you go about object instantiation?

 

A factory or builder in DD terms

[dgoosens]

Well there are some places where a singleton comes in handy... doesn't it ?

 

MrAdam talks about ZF...

So Zend_Registry is quite useful I believe

 

I find it very useful to make sure there is only one instance for the DB connection.

 

I know you have to be careful with them though and don't use them everywhere...

[Daniel0]

I find it very useful to make sure there is only one instance for the DB connection.

 

So what happens when you need *drumroll*... two connections?

Answer: You're screwed.

 

And what happens when you need to do unit testing, but the choice of adapter is hardcoded and you want to mock it?

Answer: You're screwed.

 

And what happens when you want to change from MySQLWhatever to PostregeSQLWhatever, but the choice of adapter is hardcoded?

Answer: You're screwed.

[Garethp]

What are Signletons?

[dgoosens]

So what happens when you need *drumroll*... two connections?

Answer: You're screwed.

although I don't see the point of having two connections for the same DB...

in that case you would not work with a singleton... obviously...

 

And what happens when you need to do unit testing, but the choice of adapter is hardcoded and you want to mock it?

Answer: You're screwed.

nope...

cuz if you configure you're application correctly, let's say with Zend_Config for instance, you would be able to set up one configuration for testing, and another for production...

 

And what happens when you want to change from MySQLWhatever to PostregeSQLWhatever, but the choice of adapter is hardcoded?

Answer: You're screwed.

sorry, but you're wrong here...

Idealy you would not hardcode this kind of stuff in your models.

Instead you would use an abstraction layer to handle this...

Ergo, one modification in your config file and you can jump from a MySQL to a PostgreSQL or to whatever DB you'd like.

[ignace]

What are Signletons?

 

A Singleton is a design pattern defined by the Gang of Four (GoF) to keep only one instance of an object.

 

class Singleton {
    private static $_instance = null;
    
    private function __construct() {} // disable instantiation
    private function __clone() {} // disabe cloning
    
    public static function getInstance() {
        if (null === self::$_instance) {
            self::$_instance = new self();
        }
        return self::$_instance;
    }
}

 

And that's his implementation.

[Daniel0]

And what happens when you need to do unit testing, but the choice of adapter is hardcoded and you want to mock it?

Answer: You're screwed.

nope...

cuz if you configure you're application correctly, let's say with Zend_Config for instance, you would be able to set up one configuration for testing, and another for production...

 

MysqlStuffBlaBla::getInstance()

 

That's a singleton.

 

I suppose you could do this:

$adapter = 'Mysql';
$class = $adapter . 'StuffBlaBla';
$foo = $class::getInstance();
// or
$foo = call_user_func(array($adapter . 'StuffBlaBla, 'getInstance'));

 

But that's some ugly looking shit.

 

I think you're talking about a factory.

[dgoosens]

And what happens when you need to do unit testing, but the choice of adapter is hardcoded and you want to mock it?

Answer: You're screwed.

nope...

cuz if you configure you're application correctly, let's say with Zend_Config for instance, you would be able to set up one configuration for testing, and another for production...

 

MysqlStuffBlaBla::getInstance()

 

That's a singleton.

 

I suppose you could do this:

$adapter = 'Mysql';
$class = $adapter . 'StuffBlaBla';
$foo = $class::getInstance();
// or
$foo = call_user_func(array($adapter . 'StuffBlaBla, 'getInstance'));

 

But that's some ugly looking shit.

 

I think you're talking about a factory.

 

oups...

you're right...

Zend_Db is a factory...

 

sorry about that...