Re: [boost] [math] RFC: comparison function objects

From: Alberto Ganesh Barbati (abarbati_at_[hidden])
Date: 2006-04-24 12:47:18

Andy Little ha scritto:
> BTW An alternate signature for the  function:
> 
> template <typename T>
> struct compare_absolute_error /*not derived from binary_function!*/ {
>  T eps;
> compare_absolute_error(T eps_) : eps(eps_) {}
> 
> //Signature as thus to prevent too many conversions
> template <typename T1, typename T2>
>  bool operator()(T1 const & x, T2  const & y) const { return abs(x - y) < eps; }
>  };
> 
> // ............. possible useage :
> 
> compare_absolute_error<int> comp(1);
> 
> int  pixel_x =100;
> float current_pos_x = 100.5;
> 
> bool grabbed = comp(current_pos_x, pixel_x);
> 

The idea is nice, but in this particular case I think the "fixed"
version is more suitable. First: the user can be sure about what
approximation is going to be used for the comparison (in the realm of
floating point, it's a big help). Second: knowing the type in advance
allows you to deal correctly with corner cases (infinities, denorm,
etc.). With the member-template approach that you suggest you would have
to handle more cases and it might easily get tedious.

Ganesh