Why can’t the above-stated operators be overloaded?

Important Points about Operator Overloading

1. sizeof Operator

This returns the size of the object or datatype entered as the operand. This is evaluated by the compiler and cannot be evaluated during runtime. The proper incrementing of a pointer in an array of objects relies on the sizeof operator implicitly. Altering its meaning using overloading would cause a fundamental part of the language to collapse.

2. typeid Operator

This provides a CPP program with the ability to recover the actually derived type of the object referred to by a pointer or reference. For this operator, the whole point is to uniquely identify a type. If we want to make a user-defined type ‘look’ like another type, polymorphism can be used but the meaning of the typeid operator must remain unaltered, or else serious issues could arise.

3. Scope resolution (::) Operator

This helps identify and specify the context to which an identifier refers by specifying a namespace. It is completely evaluated at runtime and works on names rather than values. The operands of scope resolution are note expressions with data types and CPP has no syntax for capturing them if it were overloaded. So it is syntactically impossible to overload this operator.

4. Class member access operators (.(dot), .* (pointer to member operator))

The importance and implicit use of class member access operators can be understood through the following example:

Example:

C++

// C++ program to demonstrate operator overloading
// using dot operator
#include <iostream>
using namespace std;
 
class ComplexNumber {
private:
    int real;
    int imaginary;
 
public:
    ComplexNumber(int real, int imaginary)
    {
        this->real = real;
        this->imaginary = imaginary;
    }
    void print() { cout << real << " + i" << imaginary; }
    ComplexNumber operator+(ComplexNumber c2)
    {
        ComplexNumber c3(0, 0);
        c3.real = this->real + c2.real;
        c3.imaginary = this->imaginary + c2.imaginary;
        return c3;
    }
};
int main()
{
    ComplexNumber c1(3, 5);
    ComplexNumber c2(2, 4);
    ComplexNumber c3 = c1 + c2;
    c3.print();
    return 0;
}

Output

5 + i9

Explanation:

The statement ComplexNumber c3 = c1 + c2; is internally translated as ComplexNumber c3 = c1.operator+ (c2); in order to invoke the operator function. The argument c1 is implicitly passed using the ‘.’ operator. The next statement also makes use of the dot operator to access the member function print and pass c3 as an argument.

Besides, these operators also work on names and not values and there is no provision (syntactically) to overload them.

5. Ternary or conditional (?:) Operator

The ternary or conditional operator is a shorthand representation of an if-else statement. In the operator, the true/false expressions are only evaluated on the basis of the truth value of the conditional expression.

conditional statement ? expression1 (if statement is TRUE) : expression2 (else)

A function overloading the ternary operator for a class say ABC using the definition

ABC operator ?: (bool condition, ABC trueExpr, ABC falseExpr);

would not be able to guarantee that only one of the expressions was evaluated. Thus, the ternary operator cannot be overloaded.

Operator Overloading in C++

in C++, Operator overloading is a compile-time polymorphism. It is an idea of giving special meaning to an existing operator in C++ without changing its original meaning.

In this article, we will further discuss about operator overloading in C++ with examples and see which operators we can or cannot overload in C++.