#include <string>
#include <memory>
#include <cassert>
#include <iostream>
 
class A
{
public:
    virtual ~A() = default;
    virtual std::string foo(int x) const
    {
        return "A";
    }
};
 
void testA()
{
    A a;
    assert(a.foo(10) == "A");
}
 
class B: public A
{
public:
    std::string foo() const override
    {
        return "B";
    }
};
 
void testB()
{
    B b;
    assert(b.foo() == "B");
}
 
void real_code()
{
    std::unique_ptr<A> ptr(new B);
    std::cout << ptr->foo(10) << std::endl;
}
 
int main() {
	// your code goes here
	testA();
	testB();
	real_code();
	return 0;
}

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