Why Make Private Methods Virtual in C ?

Private Virtual Methods in C

In object-oriented programming, a virtual method is a member function that can be overridden by subclasses. While it's common for virtual methods to be public or protected, they can also be declared private. But what's the advantage of doing so?

In the code snippet from an open source C project, you've observed that two private methods are declared virtual: childAllowed and createElement. To shed light on this practice, let's explore the benefits of making private methods virtual.

Herb Sutter's Guidelines on Virtual Methods

According to software expert Herb Sutter, the preferred approach is to make virtual functions private. He explains that this strategy allows derived classes to override the function and customize its behavior as needed, without exposing them directly to be invoked by derived classes' code.

Benefits of Private Virtual Methods

Making a private method virtual provides several advantages:

• Encapsulation: By keeping the method private, it remains accessible only within the class hierarchy, enhancing encapsulation and maintaining the class's integrity.
• Customization without Exposure: Derived classes can selectively override virtual methods without exposing the method's implementation details, promoting flexibility while ensuring that the original method's interface remains consistent.
• Maintenance and Extensibility: Private virtual methods make it easier to maintain and extend the class hierarchy in the future. If a new customization is needed, a derived class can simply override the virtual method, without affecting the behavior of other classes that don't require the customization.

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