【程序设计】6大设计原则之依赖倒置

依赖倒置原则（Dependence Inversion Principle，DIP）：

1. 代码设计要依赖于抽象接口，不要依赖于具体实现。

2. 通过面向抽象的编程方式来降低类之间的耦合，便于扩展。

反例示例：

class LuckyDrawController {
  prizeRandom(users: User[], count: number): User[] {
    ...
  }
 
  prizeWeight(users: User[], count: number): User[] {
    ...
  }
}

UML类图：

代码实现：

class User {
  name: string; // 用户名
  level: number; // 会员等级
  active: number; // 活跃值
  constructor(name: string, level: number, active: number) {
    this.name = name;
    this.level = level;
    this.active = active;
  }
}

抽奖接口：传入所有参加抽奖的用户，返回得奖的用户

interface ILuckyDraw {
  prize(users: User[], count: number): User[];
}

全随机抽奖类

class RandomLuckyDraw implements ILuckyDraw {
  prize(users: User[], count: number): User[] {
    // 洗牌
    const shuffleUsers = _.shuffle(users);
    // 随机抽取三位用户
    return _.sampleSize(shuffleUsers, count);
  }
}

按权重抽象

class WeightLuckyDraw implements ILuckyDraw {
  prize(users: User[], count: number): User[] {
    // 排序
    const sortUsers = _.orderBy(users, ["level", "active"], ["desc", "desc"]);
    // 抽取前三位
    return _.take(sortUsers, count);
  }
}

运行示例：

import { RandomLuckyDraw, WeightLuckyDraw, User } from "./DIP";
 
// 生成随机用户
let users = [];
for (let i = 0; i < 10; i++) {
  const user = new User(
    Mock.Random.cname(),
    Mock.Random.integer(0, 10),
    Mock.Random.integer(50, 100)
  );
  users.push(user);
}
 
// 随机抽奖
const randomLuckyDraw = new RandomLuckyDraw();
const winners1 = randomLuckyDraw.prize(users, 3);
console.log(winners1);
 
// 权重抽奖
const weightLuckyDraw = new WeightLuckyDraw();
const winners2 = weightLuckyDraw.prize(users, 3);
console.log(winners2);

【在线代码】：依赖倒置原则演示