Example of bad implementation of a 1D point class

pointbad.cpp

class PointBad {
  private:
    int x_;
  public:
    PointBad(int x) : x_(x) {}

    int GetX() {
        return this->x_;
    }
};

void f() {
    PointBad const p(5);
    std::cout << p.GetX(); // Compiler error: calling member function on const instance
}