RE: Singleton / Function

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From: Cowboy (Gregory A. Beamer) - MVP (NoSpamMgbworld_at_comcast.netNoSpamM)
Date: 12/02/04 

Date: Thu, 2 Dec 2004 13:33:03 -0800

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!
***************************
"Christian" wrote:
> 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

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