1using System;
 2
 3namespace jive
 4{
 5  static public class FuncExtensions
 6  {
 7    static public readonly object mutex = new object();
 8
 9    static public Func<T> memoize<T>(this Func<T> item) where T : class
10    {
11      T the_implementation = null;
12      return () =>
13      {
14        if (null == the_implementation)
15        {
16          lock (mutex)
17          {
18            if (null == the_implementation)
19            {
20              the_implementation = item();
21            }
22          }
23        }
24        return the_implementation;
25      };
26    }
27  }
28}