Mateusz Pusz

> Could you point me to where in the code the ordering predicate is for units and for quantities? Playing around with the units ordering predicate might help me form...

Now, as all of the entities (tag types) have to be `final` to enforce their uniqueness, we should no longer depend on user-provided symbols (which might not be globally unique)...

We could implement those as: ```cpp inline constexpr struct height : quantity_spec {} height; inline constexpr struct depth : decltype(height) {} height; inline constexpr struct altitude : decltype(height) {} height;...

> To me, the "one" of an algebra is the identity object of the multiplication group Yes, this was the original intent suggested by one of the ISO members. But...

> So maybe that should be part of something like a representation_traits instead. We have something similar already: https://github.com/mpusz/units/blob/49ba4891183e65263ad6cd0f2a8ea334d1f9faa0/src/core/include/units/customization_points.h#L56-L89 The question is do we want to keep it and if...

Just to elaborate a bit more on what I have in mind here: 1. The physical quantities library should work with any numeric-like representation type. 2. Right now, there is...

> As for acceptable types for the representation of a quantity, I believe [std::is_arithmetic](https://en.cppreference.com/w/cpp/types/is_arithmetic) does the job. No, it does not. It limits the type only to fundamental types. We...

> You may want to have a look at the [compositional numbers library](https://github.com/johnmcfarlane/cnl), which composes actual "number-like" types from various aspects. Yes, I am aware of that and other projects...

Well, I think that an LA vector is not the only way to model a vector quantity, and maybe not even a good choice at all. I can imagine a...

> Is there any other concept than the linear algebra concept of vectors? If so, there may be a need to clarify the concept of a "vector quantity", as I...