#include<iostream>
#include<sstream>
struct A{
	int impl_;
};
 
std::ostringstream& operator<<(std::ostringstream& oss, A const& a){
	oss << "A(" << a.impl_ << ")";
	return oss;
}
 
std::ostringstream& operator<<(std::ostringstream&& oss, A const& a){
	return operator<<(std::move(oss), a);
//	oss << "A(" << a.impl_ << ")";
//	return oss;
}
 
 
int main() {
 
	A a{2};
	{// C++98 way
		std::ostringstream oss;
		oss << a;
		std::cout << oss.str() << std::endl; // prints "A(2)", ok"
	}
	{// possible with C++11, because of the rvalue overload
		std::cout << (std::ostringstream() << a).str() << std::endl; //prints "A(2)", ok
	}
}

I2luY2x1ZGU8aW9zdHJlYW0+CiNpbmNsdWRlPHNzdHJlYW0+CnN0cnVjdCBBewoJaW50IGltcGxfOwp9OwoKc3RkOjpvc3RyaW5nc3RyZWFtJiBvcGVyYXRvcjw8KHN0ZDo6b3N0cmluZ3N0cmVhbSYgb3NzLCBBIGNvbnN0JiBhKXsKCW9zcyA8PCAiQSgiIDw8IGEuaW1wbF8gPDwgIikiOwoJcmV0dXJuIG9zczsKfQoKc3RkOjpvc3RyaW5nc3RyZWFtJiBvcGVyYXRvcjw8KHN0ZDo6b3N0cmluZ3N0cmVhbSYmIG9zcywgQSBjb25zdCYgYSl7CglyZXR1cm4gb3BlcmF0b3I8PChzdGQ6Om1vdmUob3NzKSwgYSk7Ci8vCW9zcyA8PCAiQSgiIDw8IGEuaW1wbF8gPDwgIikiOwovLwlyZXR1cm4gb3NzOwp9CgoKaW50IG1haW4oKSB7CgkKCUEgYXsyfTsKCXsvLyBDKys5OCB3YXkKCQlzdGQ6Om9zdHJpbmdzdHJlYW0gb3NzOwoJCW9zcyA8PCBhOwoJCXN0ZDo6Y291dCA8PCBvc3Muc3RyKCkgPDwgc3RkOjplbmRsOyAvLyBwcmludHMgIkEoMikiLCBvayIKCX0KCXsvLyBwb3NzaWJsZSB3aXRoIEMrKzExLCBiZWNhdXNlIG9mIHRoZSBydmFsdWUgb3ZlcmxvYWQKCQlzdGQ6OmNvdXQgPDwgKHN0ZDo6b3N0cmluZ3N0cmVhbSgpIDw8IGEpLnN0cigpIDw8IHN0ZDo6ZW5kbDsgLy9wcmludHMgIkEoMikiLCBvawoJfQp9