Exposing map of all units about units

[phlptp]

I had thought about this before. In general I didn't want to include the <unordered_map> header in units.hpp and having that symbol be exposed would lead to some complications in other libraries I use units in that generate shared libraries.

What I had thought about was adding a little wrapper in the detail::testing namespace defined at the bottom of the units.hpp file that just returned a const reference to some of the main maps, but only if the ENABLE_UNIT_TESTING or some other compile time define was enabled. I will probably need this at some point for additional testing.

[Hunter522]

Yeah that was one drawback I noticed with including <unordered_map>, unnecessarily bloating your include file. Though I just now noticed that std::unordered_map is already made available from this include tree:

• "units.hpp"
  • "units_definitions.hpp"
    • "units_decl.hpp"
      • <functional>
        • <unordered_map> tho only if __cplusplus > 201402L...or C++14 which I am using C++17

So <unordered_map> in units.hpp is actually not necessary for compilers >= C++14. Though if you're trying to target >=C++11 then I'm guessing you'd have to include it. I see no way to forward declare std::unordered_map [1]

As for the symbol conflict, I like your idea of having a separate const reference. I tried that and seemed to work fine:

units.hpp:

namespace units {
...
using smap = std::unordered_map<std::string, precise_unit>;
extern const smap& base_unit_vals_ref;

units.cpp:

static const smap base_unit_vals{
...
}

const smap& base_unit_vals_ref = base_unit_vals;

[1] https://blog.magnum.graphics/backstage/forward-declaring-stl-container-types/

[phlptp]

I am going to close this at the next release as I think this functionality is now in place