C++17 has if-statement initializers, so you can do if (auto x = re_match(foo, bar); x.has_value()) { (or x.ok() or whatever the name is of the method that

C++17 has if-statement initializers, so you can do if (auto x = re_match(foo, bar); x.has_value()) { (or x.ok() or whatever the name is of the method that tells you the validity of x)