基于C ++的说明模板语法

Question

I was looking at the following post write a boost::multi_array to hdf5 dataset and couldn't understand the syntax used for the templates in the first answer by Leo Goodstadt. Unfortunately I have not enough reputation to comment directly on the answer given there, that's why i've created this separate question.

As far as I understood this there's a struct created with a static method type() that returns the respective type.

This generic struct is then overwritten by one with a fixed type. But what exactly is written there in the curly braces , ie what is its meaning? For example, what is the meaning of the following:

{ H5::IntType type {   H5::PredType::NATIVE_CHAR
                   };  
};

within the first definition of the char-template:

template<> struct get_hdf5_data_type<char> {   
     H5::IntType type {   
         H5::PredType::NATIVE_CHAR       
    };  
};

I've copied below the essential parts of the definition of the template, but probably it's easier to look at the original post for a clear picture.

template<typename T> struct get_hdf5_data_type {   
    static H5::PredType type() {   
        //static_assert(false, "Unknown HDF5 data type"); 
        return H5::PredType::NATIVE_DOUBLE; 
    }
};
template<> struct get_hdf5_data_type<char> {   
    H5::IntType type { H5::PredType::NATIVE_CHAR };  
};
template<> struct get_hdf5_data_type<long long> {   
     H5::IntType type { H5::PredType::NATIVE_LLONG };  
};
template<> struct get_hdf5_data_type<unsigned long long> {   
     H5::IntType type { H5::PredType::NATIVE_ULLONG };  
};
template<> struct get_hdf5_data_type<int8_t> {   
    H5::IntType type { H5::PredType::NATIVE_INT8 };  
};

Answer 1

The curly syntax is initialisation

H5::IntType type    {   H5::PredType::NATIVE_CHAR       };

Is similar to

H5::IntType type = H5::PredType::NATIVE_CHAR;

I'm not familiar with H5, but the OP then uses it as hdf_data_type.type which is just refering to a particular type previously defined in your list of specialisations.

Now hdf_data_type needs to be of one of the provided template specialisations, get_hdf5_data_type<char> for instance to provide the definition for type.

The commented out static_assert in the generic template could be used as a marker that no known specialisation has been found and the object hdf_data_type is not useful.