Obviously, strings can be added with the + operator like numbers, but that has nothing to do with math but results in concatenated strings. In order to mix this with string_view, we need to convert to std::string first.

However, it is really important to note that when mixing strings and string views in code, we must never assume that the underlying string behind a string_view is zero terminated! This is why we would rather write "abc"s + string{some_string_view} than "abc"s + some_string_view.data(). Aside from that, std::string provides a member function, append, which can handle string_view instances, but it alters the string instead of returning a new one with the string view content appended.

If we want to do complex string concatenation with formatting and so on, we should however not do that piece by piece on string instances. The std::stringstream, std::ostringstream, and std::istringstream classes are much better suited for this, as they enhance the memory management while appending, and provide all the formatting features we know from streams in general. The std::ostringstream class is what we chose in this section because we were going to create a string instead of parsing it. An std::istringstream instance could have been instantiated from an existing string, which we could have then comfortably parsed into variables of other types. If we want to combine both, std::stringstream is the perfect all-rounder.