
Boost : 
From: Jens Maurer (Jens.Maurer_at_[hidden])
Date: 20010424 12:08:12
Ed Brey wrote:
>
> From: "Paul A. Bristow" <pbristow_at_[hidden]>
>
> > // math_constants.hpp <<< math constants header file  the interface.
> > namespace boost
> > {
> > namespace math_constants
> > {
> > extern const long double pi;
> > } // namespace math_constants
> > } // namespace boost
I like the templatebased interface proposed earlier better,
because it allows e.g. interval or boost::rational<int> constants.
> How is constant folding accomplished, given that the definition appears
> to be outofline?
Allowing constant folding (or not) is a qualityofimplementation issue
and should not affect the interface. (In particular, implementors
may choose to define the constants inline, but that's not what I'd
do for the generic boost implementation.)
> > cout << "pi is " << boost::math_constants::pi << endl;
> > using boost::math_constants::pi; // Needed for all constants used.
> > // recommended as useful documentation! whereas:
> > // using namespace boost::math_constants; // exposes ALL names in
> > math_constants.
> > // that could cause some name collisions!
>
> Pulling all math constants into the global namespace is indeed asking
> for trouble in general, although it would be nice to allow it as it can
> be practical within a function.
"using namespace" directives within a function scope are ok, and may
save some typing within the function. Name collisions are entirely
the responsibility of the function's author.
Jens Maurer
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