用stl容器实现特征

Question

I have a question concerning implementation of traits with stl containers.

I have some code which should work with different objects (with tensors in my case) and I have no direct access to tensor class (for instance when I use external tensor library). I try to realize all necessary properties of tensors through traits.

For example, I have a template class which should works with tensor:

template<typename Traits>
class Operator{
  typedef typename Traits::state_t state_t;
  .........
};

It means that for a particular tensor type I should specify its own traits type. For instance for SomeTensor I do:

class SomeTensorTraits{
  typedef SomeTensor state_t;
  .........
};

When I want to use other tensor type I just write another traits:

class OtherTensorTraits{
  typedef OtherTensor state_t;
  .........
};

Then I use a different tensor types in the same Operator code and it works fine.

Problems start when I want to collect a different tensors to some stl container (std::vector for example). I remind you that I don't have an access to tensor classes (so I can not make tensors derived from some base class) and I also don't want to collect TensorTraits in the container.

Thus the question is how to collect different Tensor objects through implementation of tensors in helper traits?

Appreciate your help.

Answer 1

You can use boost::any to encapsulate objects. Other way (more dirty) is to use a union that covers all cases.

Also you can create IOperator class, derive from it and use vector<IOperator&> for storing references.

Answer 2

I think you want generic traits with specialization:

template<typename T>
struct TensorTraits;

template<>
struct TensorTraits<SomeTensor>;
{
    using state_t = SomeTensor;
    // ...
};

template<>
struct TensorTraits<OtherTensor>
{
    using state_t = OtherTensor state_t;
};