RE: [boost] Boost.MathConstants: Review

From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2001-04-20 03:50:48

Matt Austern suggested:

Why not hide the macros away in a .cxx file somewhere?  I
don't see any good reason to put the actual numerical
values in the header.  It's just as good to have something
like this:
  // header file
  namespace whatever {
    ...
    extern const double pi;
    ...
  }

  // implementation file
  namespace whatever {
    const double pi = THE_ACTUAL_NUMERICAL_VALUE;
  }

Shall I produce a sample of this with actual values?
for comment by others?  Or are there other views?

I favour this because it does not require users to remember
to put pi() rather than plain pi.
Personally I find the ()s distracting from the filling in the pie.

Paul

> -----Original Message-----
> From: austern_at_[hidden] [mailto:austern_at_[hidden]]
> Sent: Thursday, April 19, 2001 8:00 PM
> To: boost_at_[hidden]
> Subject: Re: [boost] Boost.MathConstants: Review
>
>
> "Paul A. Bristow" wrote:
> >
> > > -----Original Message-----
> > > From: Ed Brey [mailto:brey_at_[hidden]]
> > > Sent: Thursday, April 19, 2001 4:19 PM
> > > To: boost_at_[hidden]
> > > Subject: [boost] Boost.MathConstants: Review
> > >
> > I am content to provide an .hpp file of this form
> >
> > > namespace boost {
> > >   namespace math {
> > >     template<typename T>
> > >     struct constants {
> > >       static T pi() {return T(3.1415...L);}
> > >     };
> > >   }
> > > }
> > >
> > > where a typical user experience would be documented as this:
> > >
> > > typedef boost::math::constants<float> c;
> > > std::cout << "Baseball and apple " << c::pi();
> >
> > as suggested (but alas not suggested in previous discussions!)
> >
> > BUT I am VERY keen to use the macro values because of the
> > long and tedious work in altering the generation program
> > to write this file with the constants embedded as above.
> > (And to write a validation program too!)
> > (And it leaves the file of macros useful for C programs -
> > I agree that should be at no extra cost to C++ users).
>
> Why not hide the macros away in a .cxx file somewhere?  I
> don't see any good reason to put the actual numerical
> values in the header.  It's just as good to have something
> like this:
>   // header file
>   namespace whatever {
>     ...
>     extern const double pi;
>     ...
>   }
>
>   // implementation file
>   namespace whatever {
>     const double pi = THE_ACTUAL_NUMERICAL_VALUE;
>   }
>
> If you find it reasonable to have macros, you can hide them
> away in that implementation file where they're out of sight.
>
> This strikes me as a cleaner solution, and I think you'd be
> hard pressed to find a platform where it made a noticable
> difference in performance.  It also has the advantage that,
> on some platforms you could initialize the numerical value
> in tricky ways that wouldn't be appropriate in a header.
> (I'm thinking of awful stuff, like using unions to control
> the exact bitwise representation.)
>
> 			--Matt
>
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