I am attempting to declare an operator override (ClassName& operator=(const ClassName& rhs)) within the header file and then define it in the .cpp, but I am running into many different errors.

My original setup:

ClassName.h:
#ifndef CLASSNAME_H
#define CLASSNAME_H
class ClassName {
  private:
    ClassName& operator=(const ClassName& rhs);
};
#endif CLASSNAME_H

ClassName.cpp:
#include "ClassName.h"
ClassName& operator=(const ClassName& rhs) {
  // some logic
}

The .cpp file errors, saying operator= must be a member function. I then tried:

ClassName.h:
#ifndef CLASSNAME_H
#define CLASSNAME_H
class ClassName {
  private:
    ClassName& operator=(const ClassName& rhs);
};
#endif CLASSNAME_H

ClassName.cpp:
#include "ClassName.h"
ClassName& ClassName::operator=(const ClassName& rhs) {
  // some logic
}

but the .cpp file now says qualified name is not allowed.

I additionally tried the solution outlined here, but the error operator= must be a member function now shows up on both declarations in the .h as well as in the .cpp.