c++ equivalent of generic type constraints

main.cpp

// c++11, c++14, c++17

#include <iostream>
#include <type_traits>

using namespace std;

class BaseClass { };
class OtherClass { };
class DerivedClass : BaseClass {};

template <typename T>
typename enable_if_t<is_base_of_v<BaseClass, T>, bool> hasBaseClass(const T& t)
{
    return true;
}

template <typename T>
typename enable_if_t<!is_base_of_v<BaseClass, T>, bool> hasBaseClass(const T& t)
{
    return false;
}

template <typename T,
    typename = enable_if_t<is_base_of_v<BaseClass, T>>>
auto only_defined_for_derived(const T& t)
{
    return 42;
}

int main()
{
    auto baseClass = BaseClass{};
    auto otherClass = OtherClass{};
    auto derivedClass = DerivedClass{};

    cout << "baseClass: " << hasBaseClass(baseClass) << endl;
    cout << "otherClass: " << hasBaseClass(otherClass) << endl;
    cout << "derivedClass: " << hasBaseClass(derivedClass) << endl;

    auto a = only_defined_for_derived(baseClass);
    //auto b = only_defined_for_derived(otherClass);      // compiler error, as expected
    auto c = only_defined_for_derived(derivedClass);

    return 0;
}

/*
Outputs:

baseClass: 1
otherClass: 0
derivedClass: 1

*/