Query about boost type traits

From: hicks (hicks_at_[hidden])
Date: 2002-05-02 01:59:57

I want to define operator * for a point type P.

template <class T>
class TPoint<T>
{
    ...
    template <class U>
    TPoint<U> operator *(U t) const;
    ...
};

template <class T>
template <class U>
TPoint<U> TPoint<T>::operator *(U t) const
    { return TPoint<U>((U)x()/t, (U)y()/t); }
   
but I only want to define this for types for which
boost::is_arithmetic<U> is true.
This is because
I also want to define operator * for an affine transformation

template <class PT, class AT>
inline Geomt::TPoint<AT> operator *
    (const Geomt::TPoint<PT>& pt, const AffHen<AT>& sAH)
{
    Geomt::TPoint<AT> pout;
    sAH.Pt(pt.x, pt.y, pout.x, pout.y);
    return pout;
}

and this sometimes conflicts with the first definition.

At the point of the first definition, type AffHen is unknown,
so I can't branch there then using type traits.  What I want to do
is leave all argument types apart from arithmentic types undefined,
to be available for later use.

Is there a well known way to do this apart from making the
affine transform the first argument?
I wonder if boost type traits can help here.

I know how to use type traits to enable compile time seperate procedures,
but not how to use it to define a procedure for some type and not others.

Craig Hicks