nholthaus / units

a compile-time, header-only, dimensional analysis and unit conversion library built on c++14 with no dependencies.

http://nholthaus.github.io/units/

MIT License

947 stars 135 forks source link

Better use of abbreviated unit identifiers #196

Open JohelEGP opened 5 years ago

JohelEGP commented 5 years ago

For a long while now, I've thought that it'd be great if we could naturally write the following.

using namespace units::literals;
using namespace units::constants;
const auto speed_limit = 90_km/h;

However, we need to write 90_km/1_h as the abbreviated unit identifiers happened to be taken up by some "tags."

What do you think about repurposing these identifiers to somewhere else, like the units::constants namespace, where they'd be declared along the lines of:

inline constexpr time::hour_t<int> h(1);

This would allow us to more naturally express units in our programs. The standard time library already allows expressing dates using the natural syntax, like 1970y/January/1. I don't see why we shouldn't follow suit.

nholthaus commented 5 years ago

Yes, this. It never crossed my mind honestly but I love the natural syntax. That's the ethos and purpose of the library in the first place.

Maybe the literals namespace is better than constants though?

JohelEGP commented 5 years ago

I had thought about it, and people using namespace units::literals; for the UDLs might find themselves having undesired clashes or accidentally using these kind of "constant literals". However, I haven't come up with something better.

nholthaus commented 5 years ago

hmm, good point. I still like inlining the real constants namespace, we can call these literal_constants or something like that. That said, I may be OK leaving the clash resolution as an exercise to the user. If you have a bunch of single letter variables or unit abbreviations as variables, you may need/want a refactor for units anyway.

On Fri, Oct 26, 2018 at 3:55 PM Johel Ernesto Guerrero Peña < notifications@github.com> wrote:

I had thought about it, and people using namespace units::literals; for the UDLs might find themselves having undesired clashes or accidentally using these kind of "constant literals". However, I haven't come up with something better.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/nholthaus/units/issues/196#issuecomment-433525374, or mute the thread https://github.com/notifications/unsubscribe-auth/AJ2HH-m6b4RqNOt623NXDpq4BmQoWEgtks5uo2jPgaJpZM4XaS3N .

JohelEGP commented 5 years ago

Yeah. literals might be good enough most of the time.

nholthaus commented 5 years ago

if not we'll just patch it out in v3.1 I suppose...

On Fri, Oct 26, 2018 at 4:14 PM Johel Ernesto Guerrero Peña < notifications@github.com> wrote:

Yeah. literals might be good enough most of the time.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/nholthaus/units/issues/196#issuecomment-433530192, or mute the thread https://github.com/notifications/unsubscribe-auth/AJ2HH3ykHZLD4xu1DDyG1SYag5YbYCR3ks5uo205gaJpZM4XaS3N .