How do I overload the increment operator so that this code becomes invalid -

Point p(2, 3);
    p;

while allowing the following -

Point p(2, 3), a(0, 0), b(1, 4);
a =   p   b;

Like in C this would be invalid -

int a = 2;
    a;

CodePudding user response：

One way you could do this is to make your operator () return a const reference. That would prevent subsequent modification of the returned value, as in a 'chained' p;.

Here's an outline version that also includes the required binary addition operator, implemented as a non-member function (as is normal):

#include <iostream>

class Point {
public:
    int x{ 0 }, y{ 0 };
    Point(int a, int b) : x{ a }, y{ b } {}
    const Point& operator  () {   x;   y; return *this; }
    Point& operator =(const Point& rhs) { x  = rhs.x; y  = rhs.y; return *this; }
};

inline Point operator (Point lhs, const Point& rhs)
{
    lhs  = rhs;
    return lhs;
}

int main()
{
    Point p(2, 3), a(0, 0), b(1, 4);
    a =   p   b; // OK: The result of the   p is passed by value (i.e. a copy)
    std::cout << a.x << " " << a.y << "\n";
//      a; // error C2678: binary '  ': no operator found which takes a left-hand operand of type 'const Point'
    return 0;
}