check if member exists using enable_if

Question

Here\'s what I\'m trying to do:

template  struct Model
{
    vector vertices ;

    #if T has a .normal member
    void transform(         


        

Answer 1

I know that it's little late, however...

typedef int Matrix;

struct NormalVertex {
    int pos;
    int normal;
};

struct Vertex {
    int pos;
};

template  struct Model
{
    typedef int No;
    typedef char Yes;

    template static decltype (declval().normal, Yes()) has_normal(U a);
    static No has_normal(...);

    vector vertices ;

    template 
    typename enable_if())) == sizeof(Yes), void>::type
    transform( Matrix m )
    {
        std::cout << "has .normal" << std::endl;
        for (auto vertex : vertices)
        {
          vertex.pos = m * vertex.pos ;
          vertex.normal = m * vertex.normal ;
        }
    }

    template 
    typename enable_if())) == sizeof(No), void>::type
    transform( Matrix m )
    {
        std::cout << "has no .normal" << std::endl;
        for (auto vertex : vertices)
        {
          vertex.pos = m * vertex.pos ;
        }
    }
} ;

int main()
{
    Matrix matrix;
    Model  normal_model;

    Vertex simple_vertex;
    Model  simple_model;

    simple_model.transform(matrix);
    normal_model.transform(matrix);

    return 0;
}