#include <cassert>
#include <iostream>
#include <type_traits>

struct Base { int value = 7; };
struct PublicChild : Base {};
class PrivateChild : Base {};

class Box {
    int value_;
public:
    explicit Box(int value) : value_(value) {}
    int value() const { return value_; }
};

int main() {
    static_assert(std::is_convertible<PublicChild*, Base*>::value, "public base");
    static_assert(!std::is_convertible<PrivateChild*, Base*>::value, "private base");
    PublicChild child;
    Box box(9);
    assert(child.value == 7);
    assert(box.value() == 9);
    std::cout << child.value << ' ' << box.value() << '\n';
}