Re: templates

From:

"Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 08 Jan 2011 04:52:09 +0100

Message-ID:

<ig8n1f$9jg$1@news.eternal-september.org>

* Chameleon, on 08.01.2011 03:17:

Is this possible?

template<int DIMENSIONS>
struct Vector
{
union {
long double elements[DIMENSIONS];
struct {long double x;
long double y;
____if DIMENSIONS==3
long double z;
____else
static const long double z = 0;
____endif
};
};
};

<code>
template< int n >
class Vector
{
private:
     double values_[n];

public:
     Vector(): values_() {}

     double& operator[] ( int i ) { return values_[i]; }
     double operator[] ( int i ) const { return values_[i]; }

     double& x() { return values_[0]; }
     double x() const { return values_[0]; }

     double& y() { return values_[1]; }
     double y() const { return values_[1]; }

     double& z();
     double z() const;
};

template< int n >
double& Vector<n>::z()
{
     char noZForThisDimension[2*(n - 3) + 1];
     throw 666;
}

template<>
double& Vector<3>::z() { return values_[2]; }

template< int n >
double Vector<n>::z() const
{
     static double const defaultZ = 0.0;
     return defaultZ;
}

template<>
double Vector<3>::z() const { return values_[2]; }

int main()
{
     Vector<2> v;

     v.x();
     v.y();
     //v.z();
}
</code>

Cheers & hth.,

- Alf

--
blog at <url: http://alfps.wordpress.com>