Question

I have a template class, the only template parameter is typename.

template<typename T>
class Reader{
    ...
}

Now I want to specialize it for every integer type, something like:

template<typename T - integral>
class Reader{
    //another code
}

How can I achieve this?

Answer 1

You can use a dummy std::true_type parameter

template<typename T, typename = std::true_type>
class Reader {

};

template<typename T>
class Reader<T, std::integral_constant<bool, 
                  std::is_integral<T>::value> > {
  // ...
};

Incidentally you will see this pattern used with void instead of true_type, with the specializations often using enable_if and more complicated (and SFINAE involving) conditions.