在条件宏中计算非类型模板参数

Question

我想为每个习语实现遍历2d / 3d矩阵的所有像素/体素。根据尺寸，我们有2个循环或3个循环。代码似乎是这样的：

//template class for point
template<int Dim>
struct Point{
    int _data[Dim];
    int & operator ()( int index){return _data[index];}
}

//template class for multi dimensional array
template<int Dim>
struct MatN{
    enum{DIM=Dim};
    Point<Dim> _domain; 
    std::vector<double> _data;
    double & operator ()( Point<Dim> p){//in the real implementation template specialization
       if(Dim==2)return _data[p(0)+p(1)*_domain(0)];
       else if(Dim==3)return _data[p(0)+p(1)*_domain(0)+p(2)*_domain(0)*_domain(1)];
    }
    int sizeI(){return _domain(0);}
    int sizeJ(){return _domain(1);}
    int sizeK(){return _domain(2);}
};

#define ForEach(point,mat) ForEach##mat.DIM (point,mat) //compile error

#define ForEach2(point,mat) 
Point<2> point;\
for(point(0)=0;point(0)<mat.sizeI();point(0)++)\
for(point(1)=0;point(1)<mat.sizeJ();point(1)++)

#define ForEach3(point,mat) \
Point<3> point;\
for(point(0)=0;point(0)<mat.sizeI();point(0)++)\
for(point(1)=0;point(1)<mat.sizeJ();point(1)++)\
for(point(2)=0;point(2)<mat.sizeK();point(2)++)

int main(){    
    MatN<2> m2d;
    ForEach(p2,m2d){           
        //do something (in this process, I need the pixel position for a local process so I cannot use iterator)
       //for instance
       if(p2(0)*p2(1)>100)
          m2d(p2)=1;
       else
          m2d(p2)=0;   
    }
    MatN<3> m3d;
    ForEach(p3,m3d){
        //do something
    }
}

问题是如何评估宏中的模板参数。

注意：出于依赖性原因，我不想使用boost。