JS 中的组合和 mixin

Posted 2023-02-22

【中文标题】JS 中的组合和 mixin

【英文标题】：Compostions and mixins in JS

【发布时间】：2017-06-19 08:53:29

【问题描述】：

compositions 和 mixin 遇到了一些麻烦。 例如，假设我们有一个 AHero 和 Hero1 对象。 所有英雄都可以移动，所以 AHero.move() 是一个东西。 现在，在开发的那一刻，我想添加眩晕和被击晕的可能性。所以我制作了一个看起来像这样的新对象（称为 stunTrait）：

stunned : false,
stun(),
beStun,

我决定让英雄们有可能被击晕和被击晕。所以我做了一个 mixin ： AHero 类扩展了 stunTrait（超类）。

现在我想让一个被击晕的英雄不能移动。 所以在 Ahero 中：

move()
if(this.stunned) return;
...

后来我发现 stun 是个坏主意，所以我决定停止实施 stunTrait。现在我必须在我的 Ahero 班级中找到所有眩晕的东西，这有时会很困难，如果子班用这些眩晕的东西做一些其他的事情，那就更难了。

有没有办法避免这种情况？更好的设计？

---

class Object
  constructor(x,y)
    this.x = x
    this.y = y
  


class AHero extends stunTrait(Object)
  constructor(x,y,moveSpeed)
    this.moveSpeed = moveSpeed;
  

  move()
    super.move();
    this.speed = moveSpeed;
  


class hero1 extends AHero
  constructor(x,y,moveSpeed) 


let stunTrait = function(object)
  return class extends object
    constructor(...args) 
      super(...args);

      this.stunned = false;
    

    move()
      if(this.stunned) this.speed = 0;
    
  


let hero = new hero1(40, 50, 100);
hero.stunned = true;
hero.move();
// This work, bcs AHero.move() is called before stunTrait.move()
// but if for some reason, I decide that only hero1 should have stunTrait
// So : class hero1 extends stunTrait(AHero)
// stunTrait.move() will be called after, so stunned will not be applied
// How make compostion without breaking inheritance ?

【问题讨论】：

添加了示例。感谢您的关注！

【参考方案1】：

OP 的给定设计决策旨在修改已经从 class 端实现的 move 行为。

因此stun 行为不仅负责实现其stun 特定的状态处理，它还必须决定 是否和/或如何更改move 行为的控制流。

为此，它不仅依赖于move 的现有实现，还依赖于setSpeed。

mixins 的概念确实不适合 OP 的方法，因为它只是将其他行为混合到其他对象中。但是给定的特殊情况也必须处理move 的命名冲突。这就是特质的用途。

如果在 javascript 中曾经真正支持 applicable types，它必须能够同时进行组合特征和对象组合，以及方法修改，一个可能的解决方案可能看起来类似于接下来提供一个。

const withStunBehavior = Trait.create(function (use, applicator) 

  function moveInterceptor(proceedMove, interceptor, argsArray) 
  //console.log("withStunBehavior::moveInterceptor - this.isStunned() : ", this.isStunned());
    if (this.isStunned()) 

      this.setSpeed(0);
    /* else 
      return proceedMove.call(this);
    */
    return proceedMove.call(this);
  

  applicator(function (isStunnedValue) 
    isStunnedValue = !!isStunnedValue;
  //console.log("withStunBehavior::applicator - isStunnedValue : ", isStunnedValue);

    this.beStun = function beStun () 
      isStunnedValue = true;
    ;
    this.unban = function unban () 
      isStunnedValue = false;
    ;
    this.isStunned = function isStunned () 
      return isStunnedValue;
    ;

  ).requires([

    "setSpeed",
    "move"

  ]).around(

    "move", moveInterceptor
  );
);


class AHero 
  constructor(stateValue) 
    var
      aHero = this;

    aHero.getSpeed = function getSpeed () 
      return stateValue.moveSpeed;
    ;
    aHero.setSpeed = function setSpeed (speedValue) 
      return (stateValue.moveSpeed = speedValue);
    ;

    // withStunBehavior.call(aHero);
  
  move() 
    var
      speedValue = this.getSpeed();

    if (speedValue === 0) 
      console.log("Hero does not move at all. Its speed is " + speedValue + ".");
     else 
      console.log("Hero moves with speed " + speedValue + ".");
    
    return speedValue;
  



class AHeroWithStunBehavior extends AHero 

  constructor(stateValue) 
    super(stateValue);

    withStunBehavior.call(this);
  



var
  hero = new AHero( x: 0, y: 0, moveSpeed: 200 );

console.log("\n");
console.log("hero.getSpeed() : ", hero.getSpeed());
console.log("hero.move() : ", hero.move());
console.log("\n");
console.log("hero.setSpeed(0) : ", hero.setSpeed(0));
console.log("hero.getSpeed() : ", hero.getSpeed());
console.log("hero.move() : ", hero.move());
console.log("\n");
console.log("hero.setSpeed(100) : ", hero.setSpeed(100));
console.log("hero.getSpeed() : ", hero.getSpeed());
console.log("hero.move() : ", hero.move());
console.log("\n");
console.log("hero.isStunned : ", hero.isStunned);
console.log("hero.beStun : ", hero.beStun);
console.log("hero.unban : ", hero.unban);

var
  stunningHero = new AHeroWithStunBehavior( x: 40, y: 50, moveSpeed: 130 );

console.log("\n");
console.log("stunningHero.isStunned : ", stunningHero.isStunned);
console.log("stunningHero.beStun : ", stunningHero.beStun);
console.log("stunningHero.unban : ", stunningHero.unban);
console.log("\n");
console.log("stunningHero.getSpeed() : ", stunningHero.getSpeed());
console.log("stunningHero.move() : ", stunningHero.move());
console.log("\n");
console.log("stunningHero.setSpeed(0) : ", stunningHero.setSpeed(0));
console.log("stunningHero.getSpeed() : ", stunningHero.getSpeed());
console.log("stunningHero.move() : ", stunningHero.move());
console.log("\n");
console.log("stunningHero.setSpeed(90) : ", stunningHero.setSpeed(90));
console.log("stunningHero.getSpeed() : ", stunningHero.getSpeed());
console.log("stunningHero.move() : ", stunningHero.move());
console.log("\n");
console.log("stunningHero.beStun() : ", stunningHero.beStun());
console.log("stunningHero.move() : ", stunningHero.move());
console.log("\n");
console.log("stunningHero.setSpeed(160) : ", stunningHero.setSpeed(160));
console.log("stunningHero.getSpeed() : ", stunningHero.getSpeed());
console.log("stunningHero.move() : ", stunningHero.move());
console.log("\n");
console.log("stunningHero.unban() : ", stunningHero.unban());
console.log("stunningHero.move() : ", stunningHero.move());
console.log("\n");
console.log("stunningHero.setSpeed(160) : ", stunningHero.setSpeed(160));
console.log("stunningHero.getSpeed() : ", stunningHero.getSpeed());
console.log("stunningHero.move() : ", stunningHero.move());

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【讨论】：

这是一个了不起的答案！非常感谢 Trait 对于大型应用程序来说似乎很棒，为什么它们没有更受欢迎？ github.com/traitsjs/traits.js

1/2 @hildericsb >> ... 为什么它们没有更受欢迎一点？

2/2 @hildericsb ... ES3 语言核心确实提供了。因此，大多数人没有掌握其他语言的能力和/或没有感到压力足以要求关于如何管理 JS 代码库的新（或切换）观点，它不是（甚至不是）新的最佳启动平台想法。