从模板化类定义非模板化类

Question

Let's say i've got a templated class called model. now let's declare a class within this class called texture, that requires no template arguments. How do i go about defining it so that no matter the template argument given to the Model class, the texture object is the same. This is what it looks like.

template<class T>
class Model
{
    class Texture;
};

class Model::Texture //error because model requires a template argument.
{


};

so is there anything i can do here?

Answer 1

You should have to write that this way:

template<typename T>
class Model<T>::Texture 
{
  //you should be able to use T here, even though Texture is not a template!

   T m_data;   //T here
   Texture(T data); //T here also, as the constructor parameter!

};

As Model is a class template, so here T applies to Model only. Texture is still a non-template.

Online demo

Answer 2

namespace detail {
class Texture
{

};
}

template<class T>
class Model
{
    typedef detail::Texture Texture;
};

The detail namespace would discourage users of your API from accessing that class directly. If you don't export any API, you don't have to worry about this. The typedef allows access to the non-templated class through a name qualified with the templated one.

Answer 3

You could also use a common non-templated ancestor for this:

class ModelBase
{
    class Texture;
};


template<class T>
class Model : public ModelBase
{

};

class ModelBase::Texture
{

};