This code illustrates how to 'lift' functions in C++. Lifting is the process of transforming a function into a corresponding function in a different (usually more general) setting. The term comes from functional programming and is used in that domain extensively, but can also be useful in C++.
This particular example transforms functions of signature T (U) into functions of signature optional<T> (optional<U>). That is, if for example you have a function that takes an int and returns a std::string (like std::to_string), you can turn it into a function that takes an optional<int> and returns an optional<std::string>. An empty optional on input produces an empty optional on output. A non-empty optional on input produces a non-empty optional on output and the original function is used to transform the wrapped value.
This project is released under MIT/X11 license, so feel free to do anything you like with it.