Nitpick: std::optional<T> does not exist in C++11, nor in the recently-approved C++14. It is, nevertheless, in the process of getting into the standard, and is

Nitpick: std::optional<T> does not exist in C++11, nor in the recently-approved C++14. It is, nevertheless, in the process of getting into the standard, and is already present in GCC 4.9's libstdc++ as std::experimental::optional.