Re: [Boost-users] [math][tools][units] generic libraries not genericenough

Okay that helps, yes. However, I thought this was necessarily the whole point motivating b::u, or any units library for that matter. However, when I stop to consider the whole point of b::u compile-time-type-safety, doesn't it stand to reason that some units can't necessarily find a root? Like I wouldn't want to root a m^3, this doesn't make sense to do so; even if I could, what would the unit outcome be? Although I expect I should be able to root a m^2. These are simple examples of course. On Fri, Aug 26, 2011 at 12:26 PM, Michael Fawcett

wrote:

On Fri, Aug 26, 2011 at 2:14 PM, Michael Powell wrote:

...

Okay, I'm not positive I fully understood the first question in the whole series of emails, only so far as to respond with our experience with boost::units so far. Now, I'm really very extremely positive I don't know the tangent we're on. Perhaps someone with more history and experience with boost::units could give us a run-down what the premise behind b::u is, maybe a short primer, examples, what have you, just besides the user docs. which are fine, don't get me wrong, but might help to explain some misconceptions about what b::u is all about. Because I for one thought I knew, or at least still have a grasp of an idea, but wouldn't hurt for the newcomers. Thanks...

[Please don't top post]

The basic gist of the discussion is that many generic libraries don't fully support Boost.Units because they don't support mixed type arithmetic correctly (or aren't generic enough, however people want to say it). Consider a very simple example of a hypothetical math library function "add" that purports to handle user defined types (some sort of BigInt is a popular example):

template <typename N> N add(N lhs, N rhs) { return lhs + rhs; }

Functions like this often break with Boost.Units because the result type might not necessarily be the same as the argument types (N in this case). Not only that, it doesn't allow adding two distinct types together.

To define the function such that it would work with BigInt and Boost.Units, it would have to be something like:

template BOOST_TYPEOF_TPL(LHS() + RHS()) add(LHS lhs, RHS rhs) { return lhs + rhs; }

Hopefully that helps answer your question,

--Michael Fawcett _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users