Andrey Semashev wrote:
I also had compile-time dependencies in mind when I said "lightweight". To take the example from the docs:
https://pdimov.github.io/hash2/doc/html/hash2.html#hashing_objects_user_defi...
class X { private: std::string a; int b;
// ... public: template
friend void tag_invoke( boost::hash2::hash_append_tag const&, Hash& h, Flavor const& f, X const& v ) { boost::hash2::hash_append(h, f, v.a); boost::hash2::hash_append(h, f, v.b); } }; This requires one to depend on Boost.Hash2 for hash_append_tag and hash_append. I would prefer if there was a way (properly documented and supported) to avoid this dependency entirely.
Once things stabilize, you will be allowed to copy hash_append_fwd.hpp locally (or just declare the functions yourself.) This has always been the intent, but GCC bugs and BOOST_CXX14_CONSTEXPR complicated matters. As I mentioned, we briefly considered requiring C++14 so that the latter isn't an issue, but the feedback on Slack was negative. People love C++11 for some reason or other. Either way, this still wouldn't have solved the GCC issue. https://github.com/pdimov/hash2/blob/develop/include/boost/hash2/hash_append...