Replace Temp with Query

以查询取代临时变量的方法只适用于处理某些类型的临时变量，即那些只被赋值一次，而且之后再也没有被修改的临时变量。
看下面的代码：我们可以将 price()中的临时变量 basePrice 和discountFactor 替换为查询函数。

class Order {
  constructor(quantity, item) {
    this.quantity = quantity;
    this.item = item;
  }

  get price() {
    const basePrice = this.quantity * this.item.price;
    let discountFactor = 0.98;
    if (basePrice > 1000) {
      discountFactor -= 0.03;
    }
    return basePrice * discountFactor;
  }
}

修改后如下：可以看到，修改后，price()内的代码明显更加简洁，更加容易理解。

constructor(quantity, item) {
  this.quantity = quantity;
  this.item = item;
}

get price() {
  return this.basePrice * this.discountFactor;
}

// Use this method to replace the temp variable basePrice
get basePrice() {
  return this.quantity * this.item.price;
}

// Use this method to replace the temp variable discountFactor
get discountFactor() {
  let discountFactor = 0.98;
  if (this.basePrice > 1000) {
    discountFactor -= 0.03;
  }
  return discountFactor;
}

最后，discountFactor()函数还可以进一步简化：

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get discountFactor() {
  return this.basePrice > 1000 ? 0.95 : 0.98;
}

如果是在不支持getter和setter的语言中，我们可以使用extract function的方法来实现。

constructor(quantity, item) {
  this.quantity = quantity;
  this.item = item;
}

getPrice() {
  return this.getBasePrice() * this.getDiscountFactor();
}

// Use this method to replace the temp variable basePrice
getBasePrice() {
  return this.quantity * this.item.price;
}

// Use this method to replace the temp variable discountFactor
getDiscountFactor() {
  return this.getBasePrice() > 1000 ? 0.95 : 0.98;
}

Philip

refactor-replace-temp-with-query

Replace Temp with Query