"David Greene" wrote
Andy Little wrote:
David Greene wrote
pqs::length::m - Can we also have pqs::length::meter & metre? (Can always typedef this, I suppose)
There have been a couple of requests for this. (BTW meter is acceptable by the SI , but metre is not IIRC.) The longer names work ok for units such as meters, but:
length::millimeters
is quite a handful, while:
acceleration::millimeters_div_seconds_squared acc;
is a real handful compared with:
acceleration::mm_div_s2 acc;
Sure, this is a matter of taste. I think for the base units it should be fine, though.
The problem is to get something that works well for all units, is easy to remember, has a consistent formula and is concise. When I am writing source code, I am not worried about whether a quantity is a base unit or not. I need to be able to figure out its name quickly and write it quickly too.
pqs::velocity::m_div_s - m_per_s? I know this is discussed in the documentation but again, typedefs might be nice to have.
The use of 'div' is meant to stand in for 'divided by' as laid down in 'The Guide for the international System of Units' section 7.12.
I'm open to changing the rules by which these typedefs are formed, but I would prefer a consensus around one scheme, on grounds that two entities meaning the same thing is never a good idea, also bearing in mind that it needs to be useable over a wide range of various units as shown above.
I don't see why two entities with the same meaning is necessarily a problem. That's the whole point of typedefs. If the community agrees that one interface is best, I'm find with "div" due to the official SI recommendtation.
IMO if you have two names for something its because the first was a mistake for some reason.
Output: 1 kg.m+2.s-2 - What does this mean? It wasn't clear to me when I first saw it. Why not use ^ or ** for power?
Again if there is a consensus I will add it but I guess I figured that it was redundant. Does it aid comprehensibility? :
1 kg.m^+2.s^-2
If it does I am happy to use it.
Getting rid of the "+" would help:
1 kg.m^2.s^-2
Again, if its preferred enough then I'll modify it. I should point out that ideally you wont get these format output anyway, because you assign everything to a so called named_quantity, FWIW, which should have prettier custom output. In practise its unlikely you will be serialising anonymous quantities. ( because you are usually not serialising temporaries) IOW anonymous quantities are a bit ugly, the output format reflects that.
Or better yet:
1 kg.m^2/s^2
But the latter will get you into all sorts of complexity wrt parentheses, etc.
Yep!. The dots work quite well as separators and again the format is based on the recommended useage in the SI manual which uses dots.
The kilogram rather than the gramme is a base unit in the SI. I think that the history has to do with the emergence of the SI system from the C.G.S system. Presumably they decided that the gramme from the C.G.S system was too small a unit, the mystery then being why C.G.S used centimeters in the first place. Whatever. I agree the whole thing is a logicians nightmare. I'm just the messenger...
But I don't understand why the SI "interface" commands a particular pqs implementation. From the user perspective, they don't really care. But as soon as a programmer tries to extend the framework, nightmares ensue.
I dont think electrotechnology is an extension to the SI. IMO its a different system in which bytes and time exists, but not mass, length, current etc etc. regards Andy Little