[boost] Re: utility::string_view and core::detail::string_view

Mungo Gill wrote:

In case anyone is curious how to implement support for <format> in boost::string_view by delegating to the formatter for std::string_view: https://godbolt.org/z/YsWKrEz3P

There's no way to portably forward-declare things in std (even if we discount the fact that this is explicitly called out as undefined behavior.) https://godbolt.org/z/9f5xMEPd1