using System;
using System.Collections.Generic;
 
public class Test
{
    public static void Main()
        {
        var l = new List<Union3<string, DateTime, int>>  {
                new Union3<string, DateTime, int>(DateTime.Now),
                new Union3<string, DateTime, int>(42),
                new Union3<string, DateTime, int>("test"),
                new Union3<string, DateTime, int>("one more test")
        };
            
            foreach (Union3<string, DateTime, int> union in l)
            {
                string value = union.Match(
                    str => str,
                    dt => dt.ToString("yyyy-MM-dd"),
                    i => i.ToString());
                    
                Console.WriteLine("Matched union with value '{0}'", value);
            }
        
        }       
}
 
public sealed class Union3<A, B, C>
{
        readonly A Item1;
        readonly B Item2;
        readonly C Item3;
        int tag;
 
        public Union3(A item) { Item1 = item; tag = 0; }
        public Union3(B item) { Item2 = item; tag = 1; }
        public Union3(C item) { Item3 = item; tag = 2; }
 
        public T Match<T>(Func<A, T> f, Func<B, T> g, Func<C, T> h)
        {
            switch (tag)
            {
                case 0: return f(Item1);
                case 1: return g(Item2);
                case 2: return h(Item3);
                default: throw new Exception("Unrecognized tag value: " + tag);
            }
        }
 }