std::optional (C++17)

std::optional<T> is a small wrapper that holds either a value of type T or nothing at all. It replaces sentinel values, output parameters, nullable pointers, and other ad-hoc patterns that used to encode "this function might not produce a result". The header is <optional>, the type lives in namespace std, and the entire chapter assumes C++17 or later. Compile examples with g++ -std=c++17.