Question

In specializing a class template, I would like to have one specialization target full-blown classes (complete with constructor, destructor, etc.) and one specialization target primitives (int, float, etc.). The only partial specialization I’ve seen is with targeting pointer types (via T*). Is there a way to do this?

Answer 1

You can used C++11 type_traits. Here is something to get you started, you can specialize more as needed:

#include <type_traits>
#include <iostream>

template<typename T, typename E = void>
struct A; // undefined

template<typename T>
struct A<T, typename std::enable_if<std::is_class<T>::value && !std::is_pod<T>::value>::type> {
        A() { std::cout << "I'm a class, but I'm not a pod type" << std::endl; }
};

template<typename T>
struct A<T, typename std::enable_if<std::is_class<T>::value && std::is_pod<T>::value>::type> {
        A() { std::cout << "I'm a class and a pod type" << std::endl; }
};

template<typename T>
struct A<T, typename std::enable_if<!std::is_class<T>::value>::type> {
        A() { std::cout << "I'm not a class" << std::endl; }
};

class X {};
class Y { ~Y(){} };

int main()
{
        A<X> a1;
        A<Y> a2;
        A<int> a3;
}