c++は難しい

test.cpp

#include <iostream>

class Widget {
public:
  explicit Widget(int a, int b) : m_a(a), m_b(b) {
    std::cout << "construct" << std::endl;
  }
  void echo() const {
    std::cout << m_a << std::endl;
  }
  Widget(const Widget &w) : m_a(w.m_a), m_b(w.m_b) {
    std::cout << "copy construct" << std::endl;
  }
  Widget(Widget &&w) : m_a(w.m_a), m_b(w.m_b) {
    std::cout << "move construct" << std::endl;
  }
  Widget &operator=(const Widget &w) = default;
  Widget &operator=(Widget &&w) = default;


private:
  const int m_a;
  int m_b;
};

Widget func_a(int a) {
  const Widget w(a, 1);
  if (a > 0) {
    return w;
  }
  Widget w2(a, -1);
  return w2;
}

Widget func_b(int a) {
  const Widget w(a, 1);
  return w;
}


int main(int argc, char **argv) {
#ifndef TEST2
  const Widget w1 = func_a(1);
  w1.echo();
  const Widget w2 = func_a(-1);
  w2.echo();
  const Widget w3 = func_b(2)
  w3.echo();
#else
  Widget w4(1, 2);
  w4 = func_b(2);
  w4.echo();
#endif
  return 0;
}