How Can I Effectively Overload C Member Access Operators Like -> and ->*?

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Overloading Member Access Operators: ->, .*, and More

Operator overloading is a powerful C feature that allows developers to extend the functionality of built-in operators. However, certain member access operators, such as ->, ., ->, etc., can be confusing. Let's explore the intricacies of these operators and answer some frequently asked questions.

-> Operator

The -> operator is a nonstatic member function that takes no arguments. Its return value is an object that determines the subsequent member lookup. If the return value is an object of class type, the language continues the member lookup using the drill-down behavior, chaining operator-> calls until a pointer is returned.

For example, consider the following code:

struct client { int a; };
struct proxy {
    client *target;
    client *operator->() const { return target; }
};
struct proxy2 {
    proxy *target;
    proxy &operator->() const { return * target; }
};

int main() {
    client x = { 3 };
    proxy y = { &x };
    proxy2 z = { &y };
    std::cout << x.a << y->a << z->a; // prints "333"
}

->* Operator

Unlike ->, the ->* operator does not have any special built-in behavior. When overloaded, it can take any arguments and return any type, similar to other binary operators like , -, and /.

.* and . Operators

The .* and . operators cannot be overloaded. When the left-hand side is of class type, they have predefined meanings for accessing members. Overloading these operators could introduce confusion and would not change the behavior of valid expressions.

Const Considerations

In general, only -> requires both const and non-const versions. The const operator-> should be used when the member should not be modified, such as in const objects.

Conclusion

Overloading member access operators provides greater flexibility in code design. By understanding the unique behaviors of each operator, such as the drill-down behavior of ->, and by considering const versions when appropriate, you can optimize your code and avoid runtime errors.

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