#include <iostream>
#include <iomanip>
 
class A {
public:
	A() { std::cout << "A()\n"; }
	A(const A&) { std::cout << "A(const A&)\n"; }
	A(A&&) { std::cout << "A(A&&)\n"; }
};
 
class B {
public:
	B(A a): a_(std::move(a)) { std::cout << "B(A a)\n"; }
 
	// B(const A& a): a_(a) { std::cout << "B(const A& a)\n"; }
	// B(A&& a): a_(std::move(a)) { std::cout << "B(A&& a)\n"; }
	// B(A&& a): a_(std::forward<A>(a)) { std::cout << "B(A&& a)\n"; }
private:
	A a_;
};
 
int main() {
	A a;
	B b(a);
	// B b(A());
	return 0;
}
 

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