《재구성: 기존 코드 디자인 개선》의 독서 노트

이른바 재구성(refactoring)은 이러한 과정이다. 코드의 외적 행위를 바꾸지 않는 전제에서 코드를 수정하여 프로그램의 내부 구조를 개선한다.
예제

function statement (invoice, plays) {
let totalAmount = 0;
let volumeCredits = 0;
let result = `Statement for ${invoice.customer}
`;
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)
`;
totalAmount += thisAmount;
}
result += `Amount owed is ${format(totalAmount/100)}
`;
result += `You earned ${volumeCredits} credits
`;
return result;
}

재구성

function statement (invoice, plays) {
let result = `Statement for ${invoice.customer}
`;
for (let perf of invoice.performances) {
result += ` ${playFor(perf).name}: ${usd(amountFor(perf))} (${perf.audience} seats)
`;
}
result += `Amount owed is ${usd(totalAmount())}
`;
result += `You earned ${totalVolumeCredits()} credits
`;
return result;
function totalAmount() {
let result = 0;
for (let perf of invoice.performances) {
result += amountFor(perf);
}
return result;
}
function totalVolumeCredits() {
let result = 0;
for (let perf of invoice.performances) {
result += volumeCreditsFor(perf);
}
return result;
}
function usd(aNumber) {
return new Intl.NumberFormat("en-US",
{ style: "currency", currency: "USD",
minimumFractionDigits: 2 }).format(aNumber/100);
}
function volumeCreditsFor(aPerformance) {
let result = 0;
result += Math.max(aPerformance.audience - 30, 0);
if ("comedy" === playFor(aPerformance).type) result += Math.floor(aPerformance.audience /
5);
return result;
}
function playFor(aPerformance) {
return plays[aPerformance.playID];
}
function amountFor(aPerformance) {
let result = 0;
switch (playFor(aPerformance).type) {
case "tragedy":
result = 40000;
if (aPerformance.audience > 30) {
result += 1000 * (aPerformance.audience - 30);
}
break;
case "comedy":
result = 30000;
if (aPerformance.audience > 20) {
result += 10000 + 500 * (aPerformance.audience - 20);
}
result += 300 * aPerformance.audience;
break;
default:
throw new Error(`unknown type: ${playFor(aPerformance).type}`);
}
return result;
}
}