Re: [boost] Math constants for naive and gurus? - which constants do you want?

From: Greg Colvin (gcolvin_at_[hidden])
Date: 2001-10-24 14:09:45

From: Ed Brey <edbrey_at_[hidden]>
> From: "Greg Colvin" <gcolvin_at_[hidden]>
> >
> > However, I'm still not sure why we need the various namespaces.  Why not
> > just:
> >
> >   template< typename Tag >
> >   struct constant {
> >      constant() {}
> >      operator float() const; // fully specialized for each Tag
> >      operator double() const; // fully specialized for each Tag
> >   };
> >
> >   struct pi_tag {};
> >   template<> inline constant< pi_tag >::operator float() const {
> >     return 3.14159265358979323846F;
> >   }
> >   template<> inline constant< pi_tag >::operator double() const {
> >     return 3.141592653589793238462643383279502884197;
> >   }
>
> It would certainly be nice to find a better alternative to the namespaces.  I like the thought behind the overloading suggestion.
However, it can lead to too much ambiguity, e.g.:
>
> double floor(double);
> float floor(float);
>
> double three = floor(pi);
> double two_pi_from_int = pi * 2;
> double two_pi_from_double = pi * 2.0;
>
> According to my compiler, all three statements result in ambiguity.

Right you are.  Of course
    const double pi = 3.141592653589793238462643383279502884197;
works just fine.