Memoization in C#: Complex Input

memoization_complex_input.cs

public static Func<TSource1, TSource2, TReturn> Memoize<TSource1, TSource2, TReturn>(Func<TSource1, TSource2, TReturn> func)
{
    var cache = new Dictionary<string, TReturn>();
    return (s1, s2) =>
    {
        var key = s1.GetHashCode().ToString() + s2.GetHashCode().ToString();
        if (!cache.ContainsKey(key))
        {
            cache[key] = func(s1, s2);
        }
        return cache[key];
    };
}