about overloaded functions

[hero0765]

hi:
I have a code below about overloaded functions

#include<iostream>
using namespace std;


class Integer
{

   long i;
   Integer * This() {return this;}

public:
    Integer(long ll = 0):i(ll){ cout << "Integer constructor" <<endl;}
    Integer(const Integer & h):i(h.i){ cout << "copy constructor" <<endl;}
    friend ostream & operator << (ostream & o,const Integer & a);
    friend const Integer & operator+ (const Integer &a);
    friend const Integer  operator- (const Integer &a);
    friend const Integer  operator~ (const Integer &a);
    friend  Integer * operator& (  Integer &a);

};

const Integer & operator+ (const Integer &a)
{
     cout << "+Integer" <<endl;
	 return a;


}

const Integer  operator- (const Integer &a)
{
    cout << "-Integer" <<endl;
    return Integer(-a.i);
}

const Integer  operator~ (const Integer &a)
{
    cout << "~Integer" <<endl;
    return Integer(~a.i);
}

Integer * operator& (  Integer &a)
{
    cout << "&Integer" <<endl;
    return a.This();

}

ostream & operator << (ostream & o,const Integer & a)
{

   return o << a.i ;

}

void f(Integer a)
{
   cout << -a <<endl;
   cout << +a <<endl; 
   cout << ~a <<endl;
   cout << &a <<endl;

}



int main()
{
    
	Integer a(1);
    f(a);

}

I have a question if I change the code

friend  Integer * operator& (  Integer &a);

into this

friend  Integer * operator& (  const Integer &a);

compile would report a error;
so I don't how to and when to use the const correctly.the const means what here?

[ne555]

compile would report a error

sigh, and the error is ...
The const mean that the object is constant, it can't change its state.

[coder777]

If you provide a const object you must return a pointer to a const object. The same with non const. You can provide both functions.

[hero0765]

compile would report a error
sigh, and the error is ..

error C2662: 'This' : cannot convert 'this' pointer from 'const class Integer' to 'class Integer &' Conversion loses qualifiers

[hero0765]

If you provide a const object you must return a pointer to a const object.

I have tried to change the

Integer * This() {return this;}

into

const Integer * This() {return this;}

and change the

friend  Integer * operator& (  Integer &a);

into

friend  const Integer * operator& ( const Integer &a);

After writing the code and it being compiled I am prompted with the same error.

[hero0765]

The a is a const object， ie you cannot change it
but the This() function is not declared as such ，ie to the compiler it will change the object. Hence the problem. Since the This() function does not actually change the object make it const ie

Integer * This() const {return this;}