C# pattern matching

using System;

namespace CSharpFunctional
{
    [Serializable]
    public class NoPatternException : Exception
    {
        public NoPatternException() { }
        public NoPatternException(string message) : base(message) { }
        public NoPatternException(string message, Exception inner) : base(message, inner) { }
        protected NoPatternException(
          System.Runtime.Serialization.SerializationInfo info,
          System.Runtime.Serialization.StreamingContext context)
            : base(info, context) { }
    }

    public class PatternMatching<T, TResult> where T : class
    {
        private T _Value;
        private TResult _Result;
        private bool _IsDone;

        public PatternMatching(T value)
        {
            _Value = value;
            _Result = default(TResult);
            _IsDone = false;
        }

        public PatternMatching(TResult result)
        {
            _Value = null;
            _Result = result;
            _IsDone = true ;
        }

        public static PatternMatching<T, TResult> Match(T valueToMatch)
        {
            return new PatternMatching<T, TResult>(valueToMatch);
        }
        public PatternMatching<T, TResult> Case<U>(Func<U, TResult> action) where U : class, T
        {
            return Case(action, x => true);
        }
        public PatternMatching<T, TResult> Case<U>(Func<U, TResult> action, Predicate<U> guard) where U : class, T
        {
            if(_IsDone)
            {
                return new PatternMatching<T, TResult>(_Result);
            }
            var x = _Value as U;
            if (x != null && guard(x))
            {
                return new PatternMatching<T, TResult>(action(x));
            }
            else
            {
                return new PatternMatching<T, TResult>(_Value);
            }
        }

        public PatternMatching<T, TResult> Default(Func<T, TResult> action)
        {
            if (_IsDone)
            {
                return new PatternMatching<T, TResult>(_Result);
            }
            else
            {
                return new PatternMatching<T, TResult>(action(_Value));
            }
        }

        public TResult Get()
        {
            if(!_IsDone)
            {
                throw new NoPatternException();
            }
            return _Result;
        }
    }
}