Memoize.cs

    private readonly Dictionary<object, Dictionary<Type, Dictionary<object, object>>> _memos = new Dictionary<object, Dictionary<Type, Dictionary<object, object>>>(); 
    public TOut Memoize<TIn, TOut>(TIn input, Func<TIn, TOut> expression)
    {
        if (_memos.ContainsKey(input)
            && _memos[input].ContainsKey(typeof (TIn))
            && _memos[input][typeof (TIn)].ContainsKey(expression))
            return (TOut) _memos[input][typeof (TIn)][expression];

        var result = expression(input);

        if (!_memos.ContainsKey(input))
            _memos[input] = new Dictionary<Type, Dictionary<object, object>>();

        if (!_memos[input].ContainsKey(typeof (TIn)))
            _memos[input][typeof (TIn)] = new Dictionary<object, object>();

        _memos[input][typeof (TIn)][expression] = result;

        return result;
    }