A handy implementation of fmap that is apparently missing in the standard.

fmapp.hpp

#ifndef FMAP_HPP__INCLUDE
#define FMAP_HPP__INCLUDE

#include <optional>

namespace nonstd {
	template <typename F, typename T>
	auto fmap(F f, std::optional<T> x) -> std::optional<decltype(f(std::forward<T>(*x)))> {
		return (x.has_value()) ?
			std::make_optional(f(std::forward<T>(*x))) :
			std::nullopt;
	}

	//be nice to senile programmers
	template <typename T, typename F>
	auto fmap(std::optional<T> x, F f) -> decltype(fmap(f, x)) {
		return fmap(f, x);
	}
}

#endif