class BaseClass {
};

class DerivedClass : public BaseClass {
};

void pass_shared_ptr(std::shared_ptr<BaseClass> a) {
    std::cout << "ok" << std::endl;
}

std::shared_ptr<BaseClass> bc_sh_ptr(new BaseClass());
std::shared_ptr<DerivedClass> dc_sh_ptr(new DerivedClass());

pass_shared_ptr(bc_sh_ptr);
pass_shared_ptr(dc_sh_ptr);

template <typename T> class MySharedPtr {
public:
    MySharedPtr(T *t) : t_{t} {}

private:
    T *t_;
};

void pass_my_ptr(MySharedPtr<BaseClass> a) {
    std::cout << "ok" << std::endl;
}

MySharedPtr<DerivedClass> dc_ptr(new DerivedClass());
pass_my_ptr(dc_ptr);

М>template <typename T> class MySharedPtr {
М>public:
М>    MySharedPtr(T *t) : t_{t} {}

М>private:
М>    T *t_;
М>};

М>void pass_my_ptr(MySharedPtr<BaseClass> a) {
М>    std::cout << "ok" << std::endl;
М>}
М>

template<typename Other>
MySharedPtr(const MySharedPtr<Other>& t, typename std::enable_if<std::is_base_of<T, Other>::value>::type* = nullptr);