I have a manager class, allows the user to create components via a public interface. The use can specify the component type, and pass in the construction arguments to the manager class, which will create the component object.
However, I am trying to restrict the user from creating certain component type, so their specialisations are private. But because the component type is not a function argument, I can’t figure out how to specialise it.
I am getting the error (Edit: I updated the error since the error in the MRE is different from what it was originally when I posted this question.)
template-id ‘add_component’ in declaration of primary template
#include <utility>
struct A {
A(float x) {}
};
struct B {
B(int x) {}
};
class Manager {
public:
// Allow users to add components via a public interface.
template<typename T, typename... Args>
T* add_component(Args&&... _args) {
return new T(std::forward<Args>(_args)...);
}
private:
// But there are certain components that should only be added by the manager.
template<typename... Args>
B* add_component<B>(Args&&... _args) {
return new B(std::forward<Args>(_args)...);
}
};
int main() {
Manager m;
m.add_component<A>(5.0f); // OK
m.add_component<B>(42); // Not OK
return 0;
}
>Solution :
The simplest option would be to just use constexpr if as shown below:
class Manager {
public:
template<typename T, typename... Args>
T* add_component(Args&&... _args) {
if constexpr(std::is_same_v<T, B>){
return new B(std::forward<Args>(_args)...);
}
else
{
return new T(std::forward<Args>(_args)...);
}
}
private:
};