Thread: singleton and other designs

Hello

Im facing some design problems when programming my application..

I have a class options (object) that stores all the program options and its unique (only one object of this class). Some other classes depend on it (have to be able to access data inside it).

Now I wonder what is the best approach when designing such programs..

Should I make 'class options' singleton or is it better to store a reference in each class that needs access to its data? (So I would have class &options; within each class )


I dont like passing reference of 'class options' to each class that needs to read data from it.

Which way do you prefer, what are the pros and cons?

Thanks for help

Well, I can't see much reason for having more than one instance for such a class (although maybe someone else can), so, yes, I would implement it as a singleton.

Originally Posted by ChaosEngine

as long as you're in a single-threaded environment, singleton is fine. If you're in a multi-threaded environment, singleton can cause problems.

you can create singletone that is thread safe. but you are right the classic example is not.

Originally Posted by l2u

Should I make 'class options' singleton or is it better to store a reference in each class that needs access to its data? (So I would have class &options; within each class )

why not use it as global variable?

Singleton is the Design Pattern that is over used the most.

can you provide a reason or real life examples to support this? (true interest)
what better alternatives are out there to model single resources?

Originally Posted by vart

Maybe, Because global variables create more problems than they solve?

The difference between a global variable and a static member of a singleton class is one of scope ONLY. For all intents and purposes, a static member of a class *IS* a global variable.

> For all intents and purposes, a static member of a class *IS* a global variable.

Code:

class foo
{
public:
	static int* getInstance();
private:
	static int* m_instance;
};

I'm just curious, how are either of the static members in the above example comparable to global variables?

My advice is that if you're looking for an object-oriented command line parsing model, look to a purely-OO language like Java to see how it's done there. Really, I have never taken an object-oriented approach to command line parsing before and on second thought, ChaosEngine is probably right about a singleton Options class not being the best from a design standpoint.

Originally Posted by ChaosEngine

Why not simply allow the "option" to reside wherever it is most relevant?

I wanted to keep all options that are being read from a file (user) in a special class (for instance class user_options).

I havent thought that might be a bad idea..

So you're saying it would be better to just copy options to class, where they're needed?
In this case I would have to store references to all classes that need particular options and then copy them where they belong to..

Is this a good approach?