Should quantity_point be integrated into quantity?

[JohelEGP]

And/or quantity_kind integrated into quantity, and quantity_point_kind integrated into quantity/quantity_point? (See #204).

This is the current state. The last 2 can be redundant and long:

quantity_point<dim_length, metre>,
quantity_kind<height, metre>,
quantity_point_kind<altitude, metre>.

I think these are mostly clear:

quantity<dim_length, metre>,
quantity<point<dim_length>, metre>,
quantity<height, metre>,
quantity<altitude, metre>,
quantity<point<height>, metre> (point<height> and altitude are the "same").

By integration, I mean making them partial specializations of quantity. Or generalizing quantity's Unit template parameter to accept Kinds/PointKinds.

For integrating quantity_point into quantity, a point<Unit> wrapper could me made along the lines of kind/derived_kind/point_kind.

I'm concerned about the lengthy names and numerous quantity*_casts. Although quantity_kind_cast and quantity_point_kind_cast could just be overloads of quantity_cast.

A touch of reality:

units::quantity_point<units::physical::si::dim_length, units::physical::si::metre>
units::quantity_kind<height, units::physical::si::metre>
units::quantity_point_kind<altitude, units::physical::si::metre>

units::quantity<units::physical::si::dim_length, units::physical::si::metre>
units::quantity<units::point<units::physical::si::dim_length>, units::physical::si::metre>
units::quantity<height, units::physical::si::metre>
units::quantity<altitude, units::physical::si::metre>
units::quantity<units::point<height>, units::physical::si::metre>

[mpusz]

I must say this is a really interesting observation. In this case, quantity is just a quantity of different "things". Those "things" are specified by a different Dimension type. I am not sure if "point" or "kind" should be specified as a dimension. I have to think about this for some time.

Side note: "dimension" usage in most physical units libraries is not ISO conforming anyway. The only thing that ISO defines is https://mpusz.github.io/units/glossary.html#term-dimension. It has sense, only for "derived quantities" and there is officially no such thing as a "base dimension". As for engineering purposes we already "abuse" the term dimension maybe we can extend it to also determine if we are dealing with a point or kind?

Any preferences anyone?

[JohelEGP]

They're not really dimensions, although in code they do wrap, and thus take the place of dimensions. By having different partial specializations, one can avoid overloading dimension further (quantity<Dimension, Unit>, quantity<Kind, Unit>, quantity<Point, Unit>).

[JohelEGP]

With this, quantity_point, quantity_kind and quantity_point_kind could be repurposed as concepts. I don't know how to rename Quantity yet.

[JohelEGP]

A point against:

• quantity{1s} -> ???
• quantity_point{1 * m} -> ???