Function create2

cpp_17/005_optional_optional.cpp:14–16

std::nullopt can be used to create any (empty) std::optional

 
// std::nullopt can be used to create any (empty) std::optional
auto create2(bool b) {
    return b ? std::optional<std::string>{"Godzilla"} : std::nullopt;
}
 
// std::reference_wrapper may be used to return a reference
auto create_ref(bool b) {