Le lun 01/03/2004 à 01:06, Thorsten Ottosen a écrit :

>  namespace std
>  {
>  
>  #define CNAME( Var ) Var##_constant_t
>  
>  #define OVERLOAD_CONTEXT( ConstType, FP, FPV )  > inline FP operator+( FP l, ConstType )  
        >  { return l + FPV; }                             > inline FP operator+( ConstType, 
FP r )          >  { return r + FPV; }                             > inline FP operator-( FP 
l, ConstType )          >  { return l - FPV; }                             > inline FP operat
or-( ConstType, FP r )          >  { return FPV - r; }                             > inline F
P operator*( FP l, ConstType )          >  { return l * FPV; }                             > 
inline FP operator*( ConstType, FP r )          >  { return r * FPV; }                       
      >  inline FP operator/( FP l, ConstType )          > { return l / FPV; }               
              >  inline FP operator/( ConstType, FP r )          > { return FPV / r; }       
                      >  
>  #define DEFINE_FP_CONSTANT( Name, FV, DV, LDV )     > struct CNAME( Name )                
                >  {                                                   >   CNAME( Name ) ()  
           {}                   >    operator float() const       { return FV; }       >   op
erator double() const      { return DV; }       >    operator long double() const { return LD
V; }      >  };                                                  > OVERLOAD_CONTEXT( CNAME( N
ame ), float, FV )        >  OVERLOAD_CONTEXT( CNAME( Name ), double, DV )       > OVERLOAD_C
ONTEXT( CNAME( Name ), long double, LDV ) >  const CNAME( Name ) Name;
>  
>  DEFINE_FP_CONSTANT( pi, 3.14F, 3.14232, 3.1423211223L )
>  
>  } // namespace std

Unless I'm missing something, it seems to me that the constants can only
be defined for built-in floating-point numbers. Indeed, once the
structure for a pi constant has been defined by DEFINE_FP_CONSTANT (in
the math_constant.hpp header), the user or others libraries cannot add
new values for their own numerical types.

With respect to that, I think the proposal of Daniel Frey is a lot more
interesting since it allows user-defined types and provides automatic
type deduction so that complex constants do not have to have their own
names. Being able to write "interval<double>  a = 2 * pi;" and being sure
it is mathematically correct and accurate is great.

Regards,

Guillaume



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