重构（程序框架设计）

重构第一个实例

案例目标：依照剧目和观众数量收钱和发优惠卷

剧目和账单放在JSON文件里，是两个结构体的数据组

Json起源于js语言但是被广泛用在各个数据的传输过程

键值对："key": value（键必须用双引号包裹）

数据类型：字符串、数字、布尔值(true/false)、数组([])、对象({})、null

歌剧

{
  "hamlet": { "name": "Hamlet", "type": "tragedy" },
  "as-like": { "name": "As You Like It", "type": "comedy" },
  "othello": { "name": "Othello", "type": "tragedy" }
}

账单

[
  {
    "customer": "BigCo",
    "performances": [
      {
        "playID": "hamlet",
        "audience": 55
      },
      {
        "playID": "as-like",
        "audience": 35
      },
      {
        "playID": "othello",
        "audience": 40
      }
    ]
  }
]

用以下程序来记录账单

function statement (invoice, plays) {
  let totalAmount = 0;    
  let volumeCredits = 0;
  let result = `Statement for ${invoice.customer}\n`;
  const format = new Intl.NumberFormat("en-US",
                        { style: "currency", currency: "USD",
                          minimumFractionDigits: 2 }).format;
//字体设置
  for (let perf of invoice.performances) {
//便利所有演出
    const play = plays[perf.playID];
    let thisAmount = 0;
//按照演出类型分类，阶梯计价
    switch (play.type) {
    case "tragedy":
      thisAmount = 40000;
      if (perf.audience > 30) {
        thisAmount += 1000 * (perf.audience - 30);
      }
      break;
    case "comedy":
      thisAmount = 30000;
      if (perf.audience > 20) {
        thisAmount += 10000 + 500 * (perf.audience - 20);
      }
      thisAmount += 300 * perf.audience;
      break;
    default:
        throw new Error(`unknown type: ${play.type}`);
    }
//最后算给观众的优惠
    volumeCredits += Math.max(perf.audience - 30, 0);
    // add extra credit for every ten comedy attendees
    if ("comedy" === play.type) volumeCredits += Math.floor(perf.audience / 5);

    // print line for this order
    result += ` ${play.name}: ${format(thisAmount/100)} (${perf.audience} seats)\n`;
    totalAmount += thisAmount;
  }
  result += `Amount owed is ${format(totalAmount/100)}\n`;
  result += `You earned ${volumeCredits} credits\n`;
  return result;
}

最后输出

Statement for BigCo
  Hamlet: $650.00 (55 seats)
  As You Like It: $580.00 (35 seats)
  Othello: $500.00 (40 seats)
Amount owed is $1,730.00
You earned 47 credits

对于重构来说，像是打acm的样例，写对拍，两个代码来跑，要有测试保证正确。

对于上述代码的修改，可以先把分支的switch 语句提出来,肯定会有些变量发生改变，需要注意值域

function amountFor(perf, play) {
  let thisAmount = 0;
  switch (play.type) {
  case "tragedy":
    thisAmount = 40000;
    if (perf.audience > 30) {
      thisAmount += 1000 * (perf.audience - 30);
    }
    break;
  case "comedy":
    thisAmount = 30000;
    if (perf.audience > 20) {
      thisAmount += 10000 + 500 * (perf.audience - 20);
    }
    thisAmount += 300 * perf.audience;
    break;
  default:
      throw new Error(`unknown type: ${play.type}`);
  }
  return thisAmount;
}

function statement (invoice, plays) {
  let totalAmount = 0;
  let volumeCredits = 0;
  let result = `Statement for ${invoice.customer}\n`;
  const format = new Intl.NumberFormat("en-US",
                        { style: "currency", currency: "USD",
                          minimumFractionDigits: 2 }).format;
  for (let perf of invoice.performances) {
    const play = plays[perf.playID];
    let thisAmount = amountFor(perf, play); //把原来的一坨提上去了

    // add volume credits
    volumeCredits += Math.max(perf.audience - 30, 0);
    // add extra credit for every ten comedy attendees
    if ("comedy" === play.type) volumeCredits += Math.floor(perf.audience / 5);

    // print line for this order
    result += ` ${play.name}: ${format(thisAmount/100)} (${perf.audience} seats)\n`;
    totalAmount += thisAmount;
  }
  result += `Amount owed is ${format(totalAmount/100)}\n`;
  result += `You earned ${volumeCredits} credits\n`;
  return result;

第 1 章 重构，第一个示例 | 《重构 改善既有代码的设计》