Multiton

A fairly simple example of the multiton pattern, with a private constructor, and a tracker for created objects, the name being an integer identifier.

Salient Chacteristic(s)

• A private keyed list for tracking objects
• A private constructor
• Named objects

Code

using System.Collections.Generic;
using System.Linq;

namespace DesignPatterns
{
    public class Multiton
    {
        //read-only dictionary to track multitons
        private static IDictionary<int, Multiton> _Tracker = new Dictionary<int, Multiton> { };

        private Multiton()
        {
        }

        public static Multiton GetInstance(int key)
        {
            //value to return
            Multiton item = null;
            
            //lock collection to prevent changes during operation
            lock (_Tracker)
            { 
                //if value not found, create and add
                if(!_Tracker.TryGetValue(key, out item))
                {
                    item = new Multiton();

                    //calculate next key
                    int newIdent = _Tracker.Keys.Max() + 1;

                    //add item
                    _Tracker.Add(newIdent, item);
                }
            }
            return item;
        }
    }
}