Niall Douglas wrote:
I am bothered about the approx 2 seconds per compiland that including <string> adds if no other STL is being included. In a million file codebase, that's an extra 23 days of compute time per build. It's unacceptable.
<system_error> doesn't need to include <string>. A forward declaration is enough. User code that calls message() does need to include <string> of course. // <system_error> template<class E> class char_traits; template<class T> class allocator; template<class E, class T = char_traits<E>, class A = allocator<E>> class basic_string; typedef basic_string<char> string; class error_category { public: virtual string message( int ev ) const = 0; }; error_category const& system_category(); class error_code { private: int e_; error_category const* p_; public: error_code() noexcept: e_(0), p_(&system_category()) {} string message(); }; // <string> template<class E, class T, class A> class basic_string { }; // user code int main() { error_code().message(); } We can't do this in Boost.System because it's not possible to forward-declare std::string portably, but the standard library can. Incidentally, have you measured the inclusion time of <string_view>?