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Author: ytianle

Composition⚓︎

Combine simple objects or functions to build more complex ones.

alt text

Composition - Black Box Reuse⚓︎

Object composition requires objects being composed have well-defined interfaces. Each object is treated as a "black box" that exposes certain methods or properties, while hiding its internal implementation details. This style of reuse is called "Black Box Reuse".

Advantages of Composition⚓︎

  • Flexibility: Objects can be composed at runtime, allowing for dynamic behavior changes.
  • Reusability: Able to get more complex functionality by combining simpler components.
  • Maintainability: Changes to one component do not affect others.
  • Avoids Inheritance Issues: Reduces problems associated with deep inheritance hierarchies. (Composition over Inheritance)

Example⚓︎

Let's use the above picture as an example. We have three simple objects: Human, Head, and Body.

public class Head
{
    public void Speak() => Console.WriteLine("Hello!");
}
public class Body
{
    public void Walk() => Console.WriteLine("Walking...");
}
public class Human
{
    private Head head = new Head();
    private Body body = new Body();
    public void Speak() => head.Speak();
    public void Walk() => body.Walk();
}
var person = new Human();
person.Speak();
person.Walk();

#include <iostream>
class Head {
public:
    void speak() { std::cout << "Hello!" << std::endl; }
};
class Body {
public:         
    void walk() { std::cout << "Walking..." << std::endl; }
};
class Human {
private:
    Head head;
    Body body;
public:
    void speak() { head.speak(); }
    void walk() { body.walk(); }
};
int main() {
    Human person;
    person.speak();
    person.walk();
    return 0;
}

Reference⚓︎