《重构》读书笔记【第1章重构，第一个示例，第2章重构原则】

文章目录

- 第1章重构，第一个示例
- - 1.1 重构前
  - 1.2 重构后
- 第2章重构原则
- - 2.1 何谓重构
  - 2.2 两顶帽子
  - 2.3 为何重构
  - 2.4 何时重构
  - 2.5 重构和开发过程

第1章重构，第一个示例

我这里使用的IDE是IntelliJ IDEA

1.1 重构前

plays.js

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

invoice.js

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

statement.js

import {plays} from "./plays.js";
import {invoice} from "./invoice.js";

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 = 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}`);
        }

        // 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;
}


let res = statement(invoice, plays);
console.log(res);

package.json

{
  "name": "untitled",
  "version": "1.0.0",
  "type": "module",
  "dependencies": {
  }
}

运行结果

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

1.2 重构后

plays.js

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

invoice.js

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

package.json

{
  "name": "untitled",
  "version": "1.0.0",
  "type": "module",
  "dependencies": {
  }
}

createStatementData.js

class PerformanceCalculator {
    constructor(aPerformance, aPlay) {
        this.performance = aPerformance;
        this.play = aPlay;
    }

    get volumeCredits() {
        return Math.max(this.performance.audience - 30, 0);
    }

    get amount() {
        throw new Error("subclass responsibility");
    }
}


class TragedyCalculator extends PerformanceCalculator {
    get amount() {
        let result = 40000;
        if (this.performance.audience > 30) {
            result += 1000 * (this.performance.audience - 30);
        }
        return result;
    }
}

class ComedyCalculator extends PerformanceCalculator {
    get amount() {
        let result = 30000;
        if (this.performance.audience > 20) {
            result += 10000 + 500 * (this.performance.audience - 20);
        }
        result += 300 * this.performance.audience;
        return result;
    }

    get volumeCredits() {
        return super.volumeCredits + Math.floor(this.performance.audience / 5);
    }
}

function createPerformanceCalculator(aPerformance, aPlay) {
    switch (aPlay.type) {
        case "tragedy":
            return new TragedyCalculator(aPerformance, aPlay);
        case "comedy":
            return new ComedyCalculator(aPerformance, aPlay);
        default:
            throw new Error(`unknown type: ${aPlay.type}`);
    }
}

export function createStatementData(invoice, plays) {
    const statementData = {};
    statementData.customer = invoice.customer;
    statementData.performances = invoice.performances.map(enrichPerformances);
    statementData.totalAmount = totalAmount(statementData);
    statementData.totalVolumeCredits = totalVolumeCredits(statementData);
    return statementData;

    function enrichPerformances(aPerformance) {
        const calculator = createPerformanceCalculator(aPerformance, playFor(aPerformance));
        const result = Object.assign({}, aPerformance);
        result.play = calculator.play;
        result.amount = calculator.amount;
        result.volumeCredits = calculator.volumeCredits;
        return result;
    }

    function playFor(aPerformance) {
        return plays[aPerformance.playID];
    }

    function totalAmount(data) {
        return data.performances.reduce((total, p) => total + p.amount, 0);
    }

    function totalVolumeCredits(data) {
        return data.performances.reduce((total, p) => total + p.volumeCredits, 0);
    }
}

statement.js

import {plays} from "./plays.js";
import {invoice} from "./invoice.js";
import {createStatementData} from "./createStatementData.js";

function statement(invoice, plays) {
    return renderPlainText(createStatementData(invoice, plays));
}

function renderPlainText(data) {
    let result = `Statement for ${data.customer}\n`;
    for (let perf of data.performances) {
        result += ` ${perf.play.name}: ${usd(perf.amount)} (${perf.audience} seats)\n`;
    }
    result += `Amount owed is ${usd(data.totalAmount)}\n`;
    result += `You earned ${(data.totalVolumeCredits)} credits\n`;
    return result;
}

function htmlStatement (invoice, plays) {
    return renderHtml(createStatementData(invoice, plays));
}
function renderHtml (data) {
    let result = `<h1>Statement for ${data.customer}</h1>\n`;
    result += "<table>\n";
    result += "<tr><th>play</th><th>seats</th><th>cost</th></tr>";
    for (let perf of data.performances) {
        result += ` <tr><td>${perf.play.name}</td><td>${perf.audience}</td>`;
        result += `<td>${usd(perf.amount)}</td></tr>\n`;
    }
    result += "</table>\n";
    result += `<p>Amount owed is <em>${usd(data.totalAmount)}</em></p>\n`;
    result += `<p>You earned <em>${data.totalVolumeCredits}</em> credits</p>\n`;
    return result;
}

function usd(aNumber) {
    return new Intl.NumberFormat("en-US",
        {
            style: "currency", currency: "USD",
            minimumFractionDigits: 2
        }).format(aNumber / 100);
}

let res = statement(invoice, plays);
console.log(res);
let assert_res = "Statement for BigCo\n" +
    " Hamlet: $650.00 (55 seats)\n" +
    " As You Like It: $580.00 (35 seats)\n" +
    " Othello: $500.00 (40 seats)\n" +
    "Amount owed is $1,730.00\n" +
    "You earned 47 credits\n"

console.log(res === assert_res)