Paul A Bristow wrote:
| -----Original Message----- | [mailto:boost-bounces@lists.boost.org] On Behalf Of Matt Calabrese | Sent: 21 October 2005 18:53 | To: boost@lists.boost.org | Subject: Re: [boost] Interest in dimension/unit-checking library? | | On 10/21/05, Deane Yang <deane_yang@yahoo.com> wrote: | | > But wouldn't it make sense to develop a core | dimensions/units library | > without any predefined dimensions in it and develop the SI | quantities | > library as a layer above that? | | | That's exactly what my library is. It's a general physical quantities | library with SI just also provided as a set of classifications and units | coupled with the library.
I've read this discussion with renewed interest.
This sounds like a good basis to work on, potentially meeting all the requirements from the feet-on-the-ground-SI group (almost certainly by far ^ meters-on-the-ground ? :-D the largest) but not excluding the head-in-the-astronomicals group (whose distances overflow SI units!), nor excluding the monetarily-important finance groups, not to mention the ones we have yet to conceive.
Don't forget the particle/quantam guys! Their units under-flow SI doubles! (Or at least loose some serious accuracy)
I worry that the compile times and complexity will outstrip both hardware and compilers, but the only way to find out is to try it. So I would encourage Matt to continue his efforts in this direction.
A lot of time could be saved with good header design, I assume, but there really is no way around some overhead. Maybe some sort of explicit instatiation and static linking stategy (whether in user or library) could help.
Paul
PS My gut instinct is to enforce explicit conversions - mainly as a matter of documenting intent, but I am just about persuaded that implicit can be OK, provided it is loseless. If we can have a way of highlighting when implicit conversion takes place, that could make everyone happier.
Implicit lossy conversions are the worst curse a library can inflict on the user, IMAO. Lossless is better, but I am only comfortable with promotions, I don't even like int to double very much (as it loses the guarantee of integralness). So yes, explicit only. Try putting the line "-- " just before this, it marks this as a sig, so it won't be quoted in a lot of agents (AFAIK):
Paul A Bristow Prizet Farmhouse, Kendal, Cumbria UK LA8 8AB Phone and SMS text +44 1539 561830, Mobile and SMS text +44 7714 330204 mailto: pbristow@hetp.u-net.com www.hetp.u-net.com