[C++14] copy this ptr and RVO

Either capture this or copy *this

template <typename R, typename... Args>
auto memoize(R(*fn)(Args...))
{
    std::map<std::tuple<Args...>, R> table;
    return [fn, table](Args... args) mutable -> R {
        auto argt = std::make_tuple(args...);
        auto memoized = table.find(argt);
        if(memoized == table.end())
        {
            auto result = fn(args...);
            table[argt] = result;
            return result;
        }
        else
        {
            return memoized->second;
        }
    };
}

g++ -fno-elide-constructors