optional-lite (conda): optional lite is a single-file header-only library to represent optional (nullable) objects and pass them by value. The library aims to provide a C++17-like optional for use with C++98 and later. If available, std::optional is used. There's also a simpler version, optional bare. Unlike optional lite, optional bare is limited to default-constructible and copyable types.
Keywords: cpp17|cpp98|header-only|no-dependencies|optional|optional-implementations|single-file