Using dataspaces with custom types

h5cpp makes some default assumptions about which dataspace to use for a particular type

• for the container templates std::vector and std::array a Simple dataspace of rank 1 is used

• for everything else hdf5::dataspace::Scalar is used.

However, in the case of user defined data types the user has to provide a type trait to tell h5cpp what dataspace to use for the type.

As an example we consider here a trait for a 3x3 matrix type. The C++ class template for such a class could look like this

template<typename T> class Matrix
{
  private:
    std::array<T,9> data_;
  public:

    T *data();
    const T *data() const;
};

The most natural choice for a dataspace for such a type would be a simple dataspace of shape 3x3 with fixed dimensions. To achive this we have to provide a type trait as follows

#include <h5cpp/hdf5.cpp>

namespace hdf5 {
namespace dataspace {


template<> class TypeTrait<Matrix>
{
  public:
    using DataspaceType = Simple;
    static DataspaceType create(const Matrix &)
    {
      return Simple({3,3});
    }

    const static DataspaceType & get(const Matrix &)
    {
      const static DataspaceType & cref_ = Simple({3,3});
      return cref_;
    }

    static void *ptr(Matrix &value)
    {
      return reinterpret_cast<void*>(value.data());
    }

    static const void*cptr(const Matrix &value)
    {
      return reinterpret_cast<const void*>(value.data());
    }
};
}
}