C++ code - 10 lines

Link:

C++, pasted on Jan 31:

struct A {
private:
  A(A const&) {}
};

A f();

int main() {
  A const &ref = f();
}

Output:

1
2
3

In function 'int main()':
Line 3: error: 'A::A(const A&)' is private
compilation terminated due to -Wfatal-errors.