On 7-12-2011 16:33, Paul A. Bristow wrote:
Boost.Math has always had an inconspicuous collection of useful math constants, mainly those that are used internally.
The presentation of these was as a function-template, called for example, as pi<double>().
using namespace boost::math::constants; return pi<Real>() * r * r;
This leads to some rather ugly equations and is most unpopular with scientific and engineering users.
John Maddock has now added a new cunning feature that allows the vast majority of users who just want a built-in double to get the constants quickly as plain variables. So in non-template code, users can write
using boost::math::double_constants; double area = pi * r * r;
and users can read the equations easily.
Nice. But actually I need something else too. I don't think I mailed this earlier so I use this announcement to describe this additional wish/suggestion shortly. pi<Real>() is a macro/function, but there should be a structure behind. If I want to use a templated user defined type, such as ttmath (I'm a fan of that library), I'm stuck (unless I oversee something). Because it boost::math::constants::pi<T> cannot be partially specialized because it is a function. To solve this Boost.Geometry defines a small class: template <typename T> struct define_pi { static inline T apply() { // Default calls Boost.Math return boost::math::constants::pi<T>(); } }; and a utility function: template <typename T> inline T pi() { return detail::define_pi<T>::apply(); } The structure behing can then be perfectly specialized for ttmath: template <ttmath::uint Exponent, ttmath::uint Mantissa> struct define_pi<ttmath::Big<Exponent, Mantissa> > { static inline ttmath::Big<Exponent, Mantissa> apply() { static ttmath::Big<Exponent, Mantissa> const the_pi("3.1415etc" return the_pi; } }; This works. But Boost.Math would define this "define_pi" structure, or similar, this workaround would not be necessary... Is that feasable?
Some draft detailed docs about just these new proposals are at
http://boost-sandbox.sourceforge.net/libs/math_constants/doc/html/index.html
What is the SVN repos behind? At boost sandbox I assume? Thanks, Barend