Is a Class a Template Specialization in C ?

Is a Class a Template Specialization?

In C , it can be useful to determine if a given type is a specialization of a particular class template. For instance, consider the following code:

template<class T>
struct A {};

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

Given the above code, how can we verify if CompareT is an A<> for some type *?

Solution:

Utilizing the is_specialization template metafunction, you can check if a type is a specialization of a class template. Here's an example:

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 {};

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

In the above example, is_specialization takes two arguments: T and Template. If T is a specialization of Template, is_specialization is std::true_type. Otherwise, it's std::false_type.

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