"Daniel Frey" <d.frey@gmx.de> wrote
Andy Little wrote:
"Tobias Schwinger" <tschwinger@neoscientists.org> wrote
Btw. Daniel Frey's library looks very interesting - did you take a look at it ?
I looked at it during the math constants review. I didnt look at the latest version, but I have now. Unfortunately it doesnt compile on VC7.1 but looks like a smarter version of my offering. (I guess that 's where the idea for mine came from.) OTOH it doesnt do eg double(pi) which syntax I happen to like.
Me too, but it doesn't work for generic types T. If T has several ctors that take different types (e.g. float, double, T), pi has no way to decide which cast would be appropriate.
I got around this ( I thought) in my quickie by using a traits class, but its messy... I guess. However IMO it shouldnt be convertible to anything. There needs to be some concept that it models. FWIW I would be content with , float, double long double. IOW numeric types. But ... eg FWIW my version still fails in boost::numeric::interval. This is always going to be the problem when trying to make one type maquerade as another :-(
It uses expression templates to allow "constant expressions" e.g: 'pi * two' or 'pow(two,one / twelve)'
Hm... I just had the idea of allowing a simple 'constant_<2> two;' to declare integer constants, but immediately ran into a more subtle problem involving two_value. Seems there's still something to redesign, so I have to play with this idea for some time...
A 'math constant' is expected to be pretty unexciting, which this doesnt deliver. Maybe if it was repackaged as say a quirky 'smart constant', rather than The std::math_constant it would be more gratefully received. IOW The big hurdle is that its slightly weird and dont always act like the type its supposed to replace. ( Which is why I am pretty content with my original solution.eg template <typename T> struct constant{ T const & pi; T const & e;... etc}Ok.... its not extensible (re higher in the thread) but it is simple and acts exactly as you would expect a T to always, (because it is a T);) The alternative is just a function eg pi<T>(); I guess.
Thats interesting . I need this type of thing , but its clumsy in use.
What is clumsy, what would be an improvement? Or a better syntax? Even if it seems impossible, I would like to know what others consider intuitive. If you have an idea how it should look like, please share it.
In an ideal world I guess one would be able to say e.g pow(my_num, n ,d ); and get the function template <typename T, int N, int D > T pow(T,N, D);
Here, I'm at a loss. Can you elaborate, please?
sure .. .... but of course it isnt doable in the language. (BTW the pi * pi stuff is cool !. Sorry... it appears I have been dismissive of that.) int val = my::pow(9,3,2); eg replaces std::pow( static_cast<double>(9) ,3./2) with the above signature. ( val --> 27 ) today you might do this as my::pow<9,3,2>(); Another example of using compile time constants directly in expressions point + point --> affine_point_combination<2> point + point + point --> affine_point_combination<3> etc.. point p = affine_combination<N>() / n ; //( where n == N and the exact function depends on whether n is a compile time constant and the runtime version throws an exception if n !=N ) affine_combination<N> / x ( where x is a compile time evaluable constant And x!=N) ---> Compile time Error I guess however, that this would require figuring out the type of constness of n. regards Andy Little