Singleton / Function

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Christian - 02 Dec 2004 18:29 GMT

Hi,
I have an public interface ILocal, and a private class (Local) derived from
this interface. The interface have 2 functions (GetValue() and SetValue()).
My object must be a singleton! How can i get a pointer to the unique instance
of my class!? I can't add a static function in the interface.. I can't add
global function.. I found a way.. (as describe later) but it have a better
way!??

----

The solution is to set my class "Local" public, and add a static function to
my class. I set the contructor private, to prevent anyone to instance my
class. But with this, others modules can call directly the other public
function (ex: GetValue() and SetValue() derived from ILocal). Someone tell me
that i can prevent this if i declare function like this :

public __gc class Local : public ILocal
{
///Get the singleton
static ILocalPersistence* GetLocalPersistence();

Object * ILocal::GetValue(String* _Name);
Void ILocal::SetValue(String* _Name, Object * _Value);
}

But i wasnt able to found how to implement this functions in the .cpp! All
the patterns i tried doent work!

Object * Local::ILocal::GetValue(String* _Name)
Object * Local::GetValue(String* _Name)
Object * ILocal::Local::GetValue(String* _Name)

Tell me if there are a better way to do that.. If not, what i did wrong!?
Thanks

Reply to this Message

Cowboy (Gregory A. Beamer) - MVP - 02 Dec 2004 21:33 GMT

The singleton pattern uses a private constructor a public static method and a
private static instance of itself to pass back from the method. Basic
signature (C#):

public class MySingleton : ILocal
{
private MySingleton { }
private static MySingleton _sing;
private string _val;

public MySingleton GetInstance()
{
if(_sing==null)
_sing=new MySingleton();

return _sing;
}

public string Value()
{
get
{
return _val;
}
set
{
_val=value;
}
}
}

That works for a single value that gets set. If you are creating an indexed
value, there is a variety of ways to handle it, like storing the value, by
name, in a hashtable and having the property return a single string value
from the hashtable. Since you already have the interface, you can link to an
interface method, but I am not sure you need an interface for what you are
attempting, unless you are using the Interfaces with other classes.

NOTE: If you are storing multiple values, you can create a singleton that
hosts a collection of objects instead of merely string vals.

---

Gregory A. Beamer
MVP; MCP: +I, SE, SD, DBA

***************************
Think Outside the Box!
***************************

> Hi,
> I have an public interface ILocal, and a private class (Local) derived from
[quoted text clipped - 30 lines]
> Tell me if there are a better way to do that.. If not, what i did wrong!?
> Thanks

Reply to this Message

Jon Skeet [C# MVP] - 03 Dec 2004 08:46 GMT

Cowboy (Gregory A. Beamer) - MVP <NoSpamMgbworld@comcast.netNoSpamM>
wrote:

> The singleton pattern uses a private constructor a public static method and a
> private static instance of itself to pass back from the method. Basic
[quoted text clipped - 26 lines]
> }
> }

That's not thread-safe - see
http://www.pobox.com/~skeet/csharp/singleton.html
for various thread-safe versions.

Signature

Jon Skeet - <skeet@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

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Christian - 03 Dec 2004 16:29 GMT

Thanks for your anwser!
But can you anwser to this part !?
I am right?! if yes, how to implement in cpp?!
thanks

> > ...... But with this, others modules can call directly the other public
> > function (ex: GetValue() and SetValue() derived from ILocal). Someone tell me
[quoted text clipped - 11 lines]
> > But i wasnt able to found how to implement this functions in the .cpp! All
> > the patterns i tried doent work!

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Singleton / Function

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