How to Determine Template Specialization in C ?

Determining Template Specialization

In C , it is often necessary to ascertain if a given type is a specialization of a particular class template. Consider the example below:

template <class T>
struct A {};

How can we determine if CompareT is an A<*> for some type * in the following code?

template<class CompareT>
void compare(){
   // is this A ?
   cout << is_same< A<*>, CompareT >::value;     // A<*> ????
}

int main(){
  compare< A<int> >();
}

For instance, here A should match A<*> and print 1.

Solution:

To achieve this, we can utilize a custom metafunction called is_specialization:

template <class T, template <class...> class Template>
struct is_specialization : std::false_type {};

template <template <class...> class Template, class... Args>
struct is_specialization<Template<Args...>, Template> : std::true_type {};

This metafunction returns true if T is a specialization of Template and false otherwise. To illustrate its usage:

static_assert(is_specialization<std::vector<int>, std::vector>{}, "");
static_assert(!is_specialization<std::vector<int>, std::list>{}, "");

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