c++ implement "Class"

Question

in java,i can use Class<? extends C> to represent a class which is a subclass of C.

es. void Test(Class<? entends C>)

But, how to implement this by cpp??

I know the cpp template,es:

template<class C>

but it can not point a subclass of some classes

Just because the syntax looks similar doesn't mean you necessarily want a template. From your description, it could be as simple as `void Test(BaseClass& obj);` for an abstract type `BaseClass`. — juanchopanza, Jun 16 '17 at 12:21
@juanchopanza The second answer in the recently applied duplicate answered the OP's question correctly IMO. — πάντα ῥεῖ, Jun 16 '17 at 12:27
If I understand your correctly (I'm not Javanese), the syntax in Java means that a certain *object* must be of *any type* that is derived from a certain *base class* `C`. Correct? — Walter, Jun 16 '17 at 12:33
@πάνταῥεῖ Really? I didn't think there was enough detail in the question to determine that. — juanchopanza, Jun 16 '17 at 12:36
@juanchopanza Yeah, it's unclear if OP want's to have a template here at all. — πάντα ῥεῖ, Jun 16 '17 at 12:37

score 2 · Answer 1 · edited Sep 27 '17 at 05:27

There are three things that come to mind.

Polymorphism: simply take as function argument a reference or pointer to the base class C.

void test(C const&obj)
{
  /*
     manipulate the object through the public interface of C
     implemented via virtual functions
  */
}

struct D:C { /* ... */ } d;    // object of class derived from C
test(d);

A template using SFINAE or static_assert in combination with std::is_base_of

template<typename T>
std::enable_if_t<std::is_base_of<C,T>::value>
test(T const&obj)
{ /* ... */ }

template<typename T>
void test(T const&obj)
{
  static_assert(std::is_base_of<C,T>::value>,"T not derived from C");
  /* ... */
}

In the future, we may have constraints and concepts

template<typename T>
requires std::Derived<T,C>
void test(T const&obj)
{
  /* ... */
}

c++ implement "Class"

1 Answers1