C++: Template problem

Interesting.

You want something like this?

struct Fiddle: Wombat {};

Wombat as is a struct temptate without a type. You can make its parameter default to int, making it a int template struct.

Kuphryn

I think you should get rid of the Foo struct since you're not using it:

template
struct Wombat {
T something;
};

But I don't see any advantage in what you're trying to do.

Quote:

Original post by rdfodra But I don't see any advantage in what you're trying to do.

Well, how could you? That's just a simplified version of what's not working. Here's some more realistic code:

struct EmptyVertex{  // Describes a vertex attribute. For use by vertex array  // code.  template<typename Type = void, int Size = 0, int Offset = 0>  struct empty_type {    static const int type =  gl_type<Type>::type;    static const int size = Size;    static const int offset = Offset;  };  // The default is that vertex attributes aren't there.  struct position_type:        public empty_type<> {};  struct normal_type:          public empty_type<> {};  struct color_type:           public empty_type<> {};  struct secondary_color_type: public empty_type<> {};  struct tex_coord_type:       public empty_type<> {};  struct weight_type:          public empty_type<> {};};// This adds a position attribute to an existing vertex type,// which may be the EmptyVertex type.template<typename Type = float,         int size = 3,         typename Base = EmptyVertex>struct PositionVertex : public Base{  // The position  Type position[size];  // 'Override' the position_type member with the correct   // information about this attribute.  struct position_type: public empty_type<Type, size, offsetof(PositionVertex, position) > {};  // The problem is that as empty_type is a member of  // EmptyVertex, the compiler doesn't appear to know that it's  // a template. It works fine if empty_type is defined outside  // EmptyVertex, but I'd rather not have to do that.};

If I understood it correctly, you just have to use empty_type's full name so that the compiler can find it, ie. qualify it with "EmptyVertex::" :

struct PositionVertex : public Base{  struct position_type: public EmptyVertex::empty_type<Type, size, offsetof(PositionVertex, position) > {};};

Have you tried struct position_type: public typename Base::empty_type {}; ?

Or even possibly struct position_type: public typename Base::template empty_type {}; (e.g. if you get parse errors about < and >)


I don't have my C++ templates book nearby (and am too lazy to check in the standard).

Can't have typename in a base class specification list Fruny.

//....template<typename Type = float,         int size = 3,         typename Base = EmptyVertex>struct PositionVertex : public Base {	Type position[size];		struct position_type : public Base::template empty_type<Type, size, offsetof(PositionVertex, position) > {};};

Quote:

Original post by snk_kid *** coolness ***

Excellent! Exactly right. I thank you. [smile]

Oh well, I had it almost right. Would you believe that the second 'typename' was a cut-and-past error? No... I guess not. [grin] [razz] [rolleyes]