Chapter 13: Problem 9

Under what circumstances should a member function be private?

Short Answer

Expert verified

Answer: A member function should be declared as private in three main circumstances: 1. When it acts as a helper function, performing specific tasks needed by one or more public member functions but not intended for direct external usage. 2. When it enforces a class invariant, maintaining conditions that must always hold true for an object of the class during its lifetime. 3. When it's necessary to control or restrict its usage, ensuring that the function's usage follows specific rules or guidelines and making it easier to reason about the class's behavior.

Step by step solution

Introduction to Private Member Functions

In object-oriented programming languages like C++, Java or Python, classes have member functions (also known as methods). These member functions can have different access specifiers like public, private, and protected that determine the visibility and accessibility of these functions. A private member function can only be accessed or called from within the class it belongs to, making it hidden and inaccessible from the outside world, including derived classes. This mechanism allows us to enforce the principle of encapsulation. We'll outline specific circumstances where private member functions should be used.

Circumstance 1: Helper Functions

One common situation where a member function should be private is when it acts as a helper function. Helper functions are those functions that perform a specific task needed by one or more public member functions but are not intended to be used directly by external users of the class. By making these helper functions private, we can keep the class's public interface clean and less prone to misuse.

Circumstance 2: Enforce Invariant

Private member functions can also be useful to enforce class invariants. Invariants are conditions that should always hold true for an object of the class during its lifetime. By making the member functions responsible for maintaining these invariants private, we can ensure that they are only called in appropriate situations, and we can maintain the integrity of the object's state.

Circumstance 3: Controlling and Restricting Usage

Another reason to make a member function private is when we want to restrict or control how it's used. When a member function is private, we can be sure that it can only be called from other member functions within the class. This provides more control over what code can access the function, making it easier to reason about the class's behavior and to ensure that the function's usage follows specific rules or guidelines.

Conclusion

In summary, a member function should be private in three main circumstances: when it acts as a helper function, when it enforces a class invariant, and when it's necessary to control or restrict its usage. By utilizing private member functions, we can create a clean, well-defined public interface, maintain the integrity of our object's state, and adhere to object-oriented design principles like encapsulation and information hiding.

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Under what circumstances should a member function be private?

Short Answer

Step by step solution

Introduction to Private Member Functions

Circumstance 1: Helper Functions

Circumstance 2: Enforce Invariant

Circumstance 3: Controlling and Restricting Usage

Conclusion

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