[boost] Re: [mpl] Math sublibrary: new version.

From: Andy Little (andy_at_[hidden])
Date: 2005-05-07 06:21:46

"Cromwell Enage" <sponage_at_[hidden]> wrote

> The following expressions are currently illegal:
>
>  rational<int_<1>,int_<0> >
>  rational_c<long,9,-5>

disallowing negative denominator seems a little harsh. 1 /  -2  is a valid 
mathematical expression.

[snip]

> I've reimplemented rational<> so that it accepts any
> numeric constants M and N for which modulus<M,N> is a
> valid expression.  That should improve its genericity.

FWIW some comments  on rational...

1) rational should have a value_type for similarity with integral_c.
( eg plus <Numerator,Denominator>::type::value_type; )

2) Because gcd is not a primitive operation( because it can be expressed solely 
in terms of others); Is there a need fo the 'impl and '::apply rigmarole. I 
think not(Same for abs,  is_negative etc.)Why is this amount of implementation 
complexity  necessary in gcd?.

3) However OTOH numerator<T> and denominator<T> need to be applicable to 
integral_c too(Otherwise there is no advantage over use of member ::denomnator) 
, but is a primitive operation; Therefore the 'impl rigmarole should be applied. 
denominator <int_<X>  >:: type   == int_<1>, numerator <int_<X>  >:: type == 
int_<X>    or whatever. It should be possible to  mix rational and integral 
parameters pretty easily.  FWIW Ive enclosed my rendition of denominator 
(hopefully boostified) in this method .

Thanks for working on it though ... ;-)

regards
Andy Little