How to Make a Copyable Object Assignable in C++

How to Make a Copyable Object Assignable in C++

Making an object copyable in C++ requires developers to make sure the object can be instantiated on the stack and that the object can be moved and copied without any problems. Making a copyable object assignable, however, is a bit more complicated and requires a few extra steps.

Step 1: Define the Assignment Operator

The first step to making a copyable object assignable is to define the assignment operator. In C++, the assignment operator is defined with the operator= syntax.

class MyObject {
public:
    MyObject& operator=(const MyObject& rhs);
};

This operator takes a const reference to an instance of the same class, which allows for assignments between two different objects.

Step 2: Implement the Assignment Operator

The next step is to actually implement the assignment operator. The implementation will likely involve copying or moving the data from the right-hand side of the assignment expression into the left-hand side.

MyObject& MyObject::operator=(const MyObject& rhs) {
    // Copy or move data from `rhs` into `this`
    return *this;
}

For objects that contain complex data such as references or pointers, it's important to consider whether a deep copy should be performed or if a shallow copy is sufficient.

Step 3: Overload the Compound Assignment Operators

Finally, the last step is to overload the compound assignment operators such as +=, -=, *=, and /=. These are simply convenience operators and can be implemented by calling the simple assignment operator inside their implementation.

MyObject& MyObject::operator+=(const MyObject& rhs) {
    *this = *this + rhs;
    return *this;
}

This completes the process of making a copyable object assignable in C++.