C++ Comma

expression1 , expression2

int x = 1, y = 2, z;

// Without parentheses, precedence binds the assignment first:
// Equivalent to: (z = x++), y;
// 1. 'z' is assigned 1.
// 2. 'x' becomes 2. 
// 3. The right operand 'y' (2) is evaluated and discarded.
z = x++, y; 

int a = 1, b = 2, c;

// With parentheses, the comma operator evaluates first:
// 1. a++ evaluates (a becomes 2). The return value (1) is discarded.
// 2. a + b evaluates (2 + 2 = 4).
// 3. c is assigned the result of the right operand (4).
c = (a++, a + b); 

// 'a' and 'b' are separate arguments (comma is a separator)
function_call(a, b); 

// Passes a single argument to the function (comma is an operator)
// Evaluates 'a', discards it, evaluates 'b', and passes 'b'
function_call((a, b)); 

class MyClass {
public:
    // Marked const so a const left-hand operand can still 
    // return a non-const reference to the right-hand operand.
    MyClass& operator,(MyClass& rhs) const {
        // Implementation details
        return rhs;
    }

    // Returns a const reference, matching the const rhs
    const MyClass& operator,(const MyClass& rhs) const {
        // Implementation details
        return rhs;
    }
};