Specializing one of two template parameters?

From: Eric Ford (eford_at_[hidden])
Date: 2001-07-07 02:09:59

I'm working on a set of coordinate classes.  Once I get them in shape,
I plan offer them here.  

The idea is I want to allow the user to define a new coordinate system
just by adding the appropriate class and specializing a constructor
for some prexisting coordinate system using the new class as input.  

Presently, I'm having a problem specializing a constructor...

I have the classes
  template<int Dimension, class TraitsType =
coordinate_system_traits<Dimension> >  class CartesianCoordinates;
  template<int Dimension, class TraitsType =
coordinate_system_traits<Dimension> >  class SphericalCoordinates;
 
Included is a constructor using a template for the argument...

  template<template<> class OtherSystemType>
  explicit CartesianCoordinates(OtherSystemType<Dimension,TraitsType>
const& x) throw();
 
Now I want to specialize that.  Using pseduo-code, I'd like to do
something like:

    template<class TraitsT>
    CartesianCoordinates<3,TraitsT >(SphericalCoordinate<3,TraitsT>
const& x)
    { ...  }

Unfortunately, that doesn't seem to work.  I really don't want to have
to specialize template<class TraitsT> CartesianCoordinates<3,TraitsT>
when I just want to add one constructor.  It appears I could also
solve this problem by eliminating the traits to the coordinate
system.  But I don't like this option either.  

Suggestions?  

Thanks,
Eford