CachedFunc.cs

// Quickly create Funcs that memoize expensive computations.
//
// In this example, ExpensiveMethod is only called once!
//
//  var cached = CachedFunc.Make ((int x, string y) => x + ExpensiveMethod (y));
//  for (int i = 0; i < 1000; i++)
//    cached (123, "hello");

public static class CachedFunc
{
    public static Func<A, B> Make<A, B> (Func<A, B> f)
    {
        var cache = new Dictionary<A, B> ();
        return a => cache.ContainsKey (a) ? cache[a] : cache[a] = f (a);
    }

    public static Func<A, B, C> Make<A, B, C> (Func<A, B, C> f)
    {
        var fTupled = Make<Tuple<A, B>, C> (tuple => f (tuple.Item1, tuple.Item2));
        return (a, b) => fTupled (Tuple.Create (a, b));
    }

    public static Func<A, B, C, D> Make<A, B, C, D> (Func<A, B, C, D> f)
    {
        var fTupled = Make<Tuple<A, B, C>, D> (tuple => f (tuple.Item1, tuple.Item2, tuple.Item3));
        return (a, b, c) => fTupled (Tuple.Create (a, b, c));
    }
}