20.2 Criticisms of Traditional OOP and Rust’s Rationale
Despite its prevalence, class-based OOP, particularly implementation inheritance, has faced criticisms that influenced Rust’s design:
- Rigid Hierarchies and Coupling: Deep inheritance chains can tightly couple classes. Changes in a base class can unexpectedly affect derived classes (the “fragile base class” problem).
- The “God Object” Problem: Overuse of inheritance can lead to complex, monolithic base classes.
- Multiple Inheritance Issues: Languages allowing inheritance from multiple base classes (like C++) face complexities like the “diamond problem,” requiring careful resolution strategies.
- Runtime Overhead: Polymorphism via virtual functions (common in C++) involves runtime dispatch (typically via vtables), incurring a performance cost compared to direct function calls.
- State Management Complexity: Understanding and managing state spread across multiple layers of an inheritance hierarchy can be challenging.
Rust’s designers opted for alternative mechanisms—primarily composition, traits, and generics—aiming to provide the benefits of OOP (like code reuse and polymorphism) while mitigating these drawbacks.