unary operator overloading using non member non friend function

[swahajali]

can anyone help me how to do unary operator overloading using non member non friend function?

[Ganado]

There's multiple unary operators in C++, each with different techniques for proper overloading.

Here's an example for the unary negation operator (-).

// Example program
#include <iostream>

class Foo {
    
  public:
    Foo(int a)
    : a(a) {}   
    
    int a;
};

// unary operator overloading using non-member, non-friend function
Foo operator-(const Foo& foo)
{
    return Foo(-foo.a);
}

int main()
{
    Foo foo(42);
    std::cout << foo.a << std::endl; // 42
    
    foo = -foo; // unary negation operator being used
    
    std::cout << foo.a << std::endl; // -42 
}