[boost] Strange snippet around operator T()

24 Nov 2008

      I was trying to find some decent way to declare named constants in
my code and ended up with the following snippet :

struct const_one
{                                                                     
  typedef int                   type;

  const_one() {}                                       
  template<class T> const_one(T const& ) {}            

  template<class T> operator type() const                              
  {                                                                    
    static type const v = {1};                                     
    return v;                                                          
  }                                                                    

  template<class T> operator T() const
  {                                        
    static T const v = {1};
    return v;
  }
};

static const const_one one_;

This allow me to have the following behavior :

int k = one_;
float e = one_;

and have proper transtyping taking place when needed.
Turning this into a macro allow to declare a large sample
of named constant that auto-transtype them when needed.

Now funny thing is that this structure allow me to do stuff like :
float k = one_ / ( 1. + three_);

Now if I remove the operator type(), I can't. But if i add a printf 
statement in this one, it is never called.
Do someone has a clue about this behavior or am I playing with some 
undefined behavior ?

TIA

-- 
___________________________________________
Joel Falcou - Assistant Professor
PARALL Team - LRI - Universite Paris Sud XI
Tel : (+33)1 69 15 66 35