Multiton pattern

The multiton pattern is a design pattern similar to the singleton, which allows only one instance of a class to be created. The multiton pattern expands on the singleton concept to manage a map of named instances as key-value pairs.

Rather than have a single instance per application (e.g. the java.lang.Runtime object in the Java programming language) the multiton pattern instead ensures a single instance per key.

using System.Collections.Generic;  
 namespace MyApplication {  
   class FooMultiton {  
     private static readonly Dictionary<object, FooMultiton> _instances = new Dictionary<object, FooMultiton>();  
     private FooMultiton() {  
     }  
     public static FooMultiton GetInstance(object key) {  
       lock (_instances) {    
         FooMultiton instance;  
         if (!_instances.TryGetValue(key, out instance)) {  
           instance = new FooMultiton();  
           _instances.Add(key, instance);  
         }  
         return instance;  
       }  
     }  
   }  
 }