可以重载赋值运算符以返回 class 的属性值吗？

Question

I wanted to return the value of a property of a class using assignment operator. I tried to fulfill this purpose. I searched a lot on the web but all of the websites I visited talked about how to overload assignment operator to do like a copy constructor of a class like this: class_t& operator=(class_t&); . Can anybody help me overload this operator to return the value of a property of a class?

This is my code:

class A_t
{
private:
  int value = 0;

public:
  int operator = (A_t);  // I failed to overload assignment operator for this
  A_t& operator = (int); // I succeeded to overload assignment operator for this
  int Value();
  void setValue(int);
};

A_t& A_t::operator = (int value)
{
  this->setValue(value);
  return *this;
}

int operator = (A_t &data)
{
  return data.value;
}

int A_t::Value() { return this->value; }
void A_t::setValue(int data) { this->value = data; }

int main()
{
    A_t object = 3;
    int value = object; // Error: cannot convert 'A_t' to 'int' in initialization

    cout << value << endl;
    return 0;
}

Answer 1

For this, you need an int operator for your class which returns the variable when being assigned to an integer. Plus the class missed the constructor required for A_t object = 3; . The corrected class looks like this,

class A_t
{
private:
    int value = 0;

public:
    //int operator = (A_t);  <-- You dont need this.
    A_t& operator = (int); // I succeeded to overload assignment operator for this
    int Value();
    void setValue(int);

    /**
     * Construct using an integer value.
     * 
     * @param val: The value to be set.
     */
    A_t(int val) : value(val) {}

    /**
     * int operator.
     * 
     * @return The value stored inside.
     */
    operator int() const
    {
        return value;
    }

    /**
     * int& operator (optional).
     *
     * @return The variable stored inside.
     */
    operator int& ()
    {
        return value;
    }
};

A_t& A_t::operator = (int value)
{
    this->setValue(value);
    return *this;
}

int A_t::Value() { return this->value; }
void A_t::setValue(int data) { this->value = data; }

int main()
{
    A_t object = 3;
    int value = object; // Error: cannot convert 'A_t' to 'int' in initialization

    cout << value << endl;
    return 0;
}

Answer 2

You can't overload operator = for this. What you can do instead is overload the implicit conversion-to- int operator inside the class:

operator int() const { return value; }

However, think carefully whether this is actually a good idea in your case. Implicit conversions should usually be avoided at all cost, because it's very error-prone (many smart people think C++ shouldn't allow defining custom implicit conversions at all.).