When should you use inheritance and when should you use composition in C++?

In C++, inheritance is used to establish an "is-a" relationship and enforce interface consistency. And composition is used to establish "contains-one" relationships, providing flexibility. Inheritance: Used when the subclass has an "is-a" relationship with the base class, such as vehicle and car. Combination: Used when the container class and component class have a "contains-one" relationship. For example, the characters in the game contain weapons, defense, and health values.

#Inheritance and composition in C++: when to use it?

In C++, inheritance and composition are two techniques for object organization and code reuse. Understanding when to use which technology is critical to writing maintainable, scalable code.

Inheritance

Inheritance allows one class (subclass) to inherit data and behavior from another class (base class). Subclasses have access to all non-private member variables and functions in the base class and can override these members to achieve different behavior.

When to use inheritance:

• When the subclass has an "is-a" relationship with the base class, for example:

  • Vehicles: cars, trucks, motorcycles
  • Animals: cats, dogs, birds

• When a specific interface needs to be enforced, e.g. :

  • Shape: round, square, triangle

Advantages:

• Provide code reusability
• Promote polymorphism (via virtual functions)
• Enforce interface consistency

Composition

Composition involves creating a class (container class) and including another class (component class) in it as its data member through a pointer or reference. Composition allows a container class to use the functionality of a component class, but the two are separate entities in memory.

When to use composition:

• When the container class has a "contains-one" relationship with the component class, for example:

  • Car: engine, tires, body
  • Computer: motherboard, CPU, memory

• When greater flexibility is required, e.g. ：

  • Modify the components of the container class at runtime
  • Use different types of components to implement the same interface

Advantages:

• Provides greater flexibility
• Allows code reuse
• Promotes modularity

Practical case:

Consider an animal simulation program in which various animals need to be represented. We can use inheritance to define a base class Animal for all animals, containing common properties (e.g. name, type). We can then create subclasses Cat, Dog, and Bird to represent specific types of animals, and override virtual functions for each subclass that describe unique behaviors .

On the other hand, consider a game engine where characters need to be represented. We can use composition to create a container class Character for each character, containing other classes as components:

class Character {
public:
  Sword* sword;  // 组件：武器
  Shield* shield;  // 组件：防御
  Health* health;  // 组件：生命值
};

In this way we can easily create characters with different weapons, defenses and health Various roles for values ​​without creating multiple inheriting classes.

In short, in C++, inheritance is mainly used to establish an "is-a" relationship and enforce interface consistency, while composition is mainly used to establish a "contains-a" relationship and provide greater flexibility. Depending on the specific requirements of your application, choosing these technologies wisely is critical to writing clear, maintainable code.

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