[Boost-users] functional/hash: hash_value with context

From: Boris Mansencal (boris.mansencal_at_[hidden])
Date: 2006-12-04 04:10:40

Hi,

A newbie question regarding functional/hash.

 I would like to use TR1 unordered_map for a 2D point custom data type.
For this, I use hash_value from Boost. But I would like to give/pass a 
context to this function : here, width & height of domain in which are 
my 2D points.
Currently, I declare theses width and height static. My code (in my cpp 
file) looks like  :

static int P_width;
static int P_height;
std::size_t hash_value(point const& p)
{
    return ((size_t)p.x()<<1)*P_width + (size_t)(p.y()<<1);
}

But this solution is not satisfactory as I can not have several 
instances of my class including the unordered_map, i.e., several domains 
of different width & height.

Is there a straightforward solution that I have overlooked ?

Regards,

Boris.