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Refactoring Examples in Swift
// Example of refactoring with protocols
// Original javascript version is from Refactoring (2nd Edition) by Martin Fowler
import Foundation
struct Play {
enum Genre {
case tragedy
case comedy
}
let name: String
let type: Genre
}
struct Performance {
let playID: String
let audience: Int
}
struct Invoice {
let customer: String
let performances: [Performance]
}
typealias Catalog = [String : Play]
struct StatementData {
struct PerformanceData {
let play: Play
let audience: Int
let amount: Int
let volumeCredits: Int
init(_ calculator: PerformanceCalculator, play: Play) {
self.play = play
audience = calculator.audience
amount = calculator.amount
volumeCredits = calculator.volumeCredits
}
}
let customer: String
let performances: [PerformanceData]
var totalVolumeCredits: Int {
return performances.reduce(0) {
result, performance in
return result + performance.volumeCredits
}
}
var totalAmount: Int {
return performances.reduce(0) {
result, performance in
return result + performance.amount
}
}
init(invoice: Invoice, plays: Catalog) {
func playFor(_ performance: Performance) -> Play {
guard let play = plays[performance.playID] else {
fatalError("Unknown play")
}
return play
}
customer = invoice.customer
performances = invoice.performances.map {
let calculator = StatementData.createPerformanceCalculator(performance: $0, play: playFor($0))
return PerformanceData(calculator, play: playFor($0))
}
}
static func createPerformanceCalculator(performance: Performance, play: Play) -> PerformanceCalculator {
switch play.type {
case .tragedy:
return TragedyCalculator(audience: performance.audience)
case .comedy:
return ComedyCalculator(audience: performance.audience)
}
}
}
protocol PerformanceCalculator {
var audience: Int { get }
var amount: Int { get }
var volumeCredits: Int { get }
}
extension PerformanceCalculator {
var volumeCredits: Int {
return max(audience - 30, 0)
}
}
struct TragedyCalculator: PerformanceCalculator {
let audience: Int
var amount: Int {
var result = 40000
if audience > 30 {
result += 1000 * (audience - 30)
}
return result
}
}
struct ComedyCalculator: PerformanceCalculator {
let audience: Int
var amount: Int {
var result = 30000
if audience > 20 {
result += 10000 + 500 * (audience - 20)
}
result += 300 * audience
return result
}
var volumeCredits: Int {
return max(audience - 30, 0) + audience / 5
}
}
func statement(invoice: Invoice, plays: Catalog) -> String {
return renderPlainText(data: StatementData(invoice: invoice, plays: plays))
}
func renderPlainText(data: StatementData) -> String {
var result = "Statement for \(data.customer)\n"
for performance in data.performances {
result += " \(performance.play.name): \(usd(performance.amount)) (\(performance.audience) seats)\n"
}
result += "Amount owed is \(usd(data.totalAmount))\n"
result += "You earned \(data.totalVolumeCredits) credits\n"
return result
}
func htmlStatement(invoice: Invoice, plays: Catalog) -> String {
return renderHTML(data: StatementData(invoice: invoice, plays: plays))
}
func renderHTML(data: StatementData) -> String {
var result = "<h1>Statement for \(data.customer)</h1>\n"
result += "<table>\n"
result += "<tr><th>play</th><th>seats</th><th>cost</th></tr>\n"
for performance in data.performances {
result += "<tr><td>\(performance.play.name)</td>"
result += "<td>\(performance.audience)</td>"
result += "<td>\(usd(performance.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
}
func usd(_ number: Int) -> String {
let format = NumberFormatter()
format.locale = Locale(identifier: "en-US")
format.numberStyle = .currency
return format.string(from: NSNumber(value: number/100)) ?? "N/A"
}
let plays: Catalog = [
"hamlet" : Play(name: "Hamlet", type: .tragedy),
"as-like" : Play(name: "As You Like It", type: .comedy),
"othello" : Play(name: "Othello", type: .tragedy)
]
let performances = [
Performance(playID: "hamlet", audience: 55),
Performance(playID: "as-like", audience: 35),
Performance(playID: "othello", audience: 40)
]
let invoice = Invoice(customer: "BigCo", performances: performances)
let text = statement(invoice: invoice, plays: plays)
print(text)
let html = htmlStatement(invoice: invoice, plays: plays)
print(html)
// Example of refactoring with subclassing
// Original javascript version is from Refactoring (2nd Edition) by Martin Fowler
import Foundation
struct Play {
enum Genre {
case tragedy
case comedy
}
let name: String
let type: Genre
}
struct Performance {
let playID: String
let audience: Int
}
struct Invoice {
let customer: String
let performances: [Performance]
}
typealias Catalog = [String : Play]
struct StatementData {
struct PerformanceData {
let play: Play
let audience: Int
let amount: Int
let volumeCredits: Int
init(_ calculator: PerformanceCalculator, play: Play) {
self.play = play
audience = calculator.audience
amount = calculator.amount
volumeCredits = calculator.volumeCredits
}
}
let customer: String
let performances: [PerformanceData]
var totalVolumeCredits: Int {
return performances.reduce(0) {
result, performance in
return result + performance.volumeCredits
}
}
var totalAmount: Int {
return performances.reduce(0) {
result, performance in
return result + performance.amount
}
}
init(invoice: Invoice, plays: Catalog) {
func playFor(_ performance: Performance) -> Play {
guard let play = plays[performance.playID] else {
fatalError("Unknown play")
}
return play
}
customer = invoice.customer
performances = invoice.performances.map {
let calculator = StatementData.createPerformanceCalculator(performance: $0, play: playFor($0))
return PerformanceData(calculator, play: playFor($0))
}
}
static func createPerformanceCalculator(performance: Performance, play: Play) -> PerformanceCalculator {
switch play.type {
case .tragedy:
return TragedyCalculator(audience: performance.audience)
case .comedy:
return ComedyCalculator(audience: performance.audience)
}
}
}
class PerformanceCalculator {
let audience: Int
var amount: Int {
fatalError("subclass responsibility")
}
var volumeCredits: Int {
return max(audience - 30, 0)
}
init(audience: Int) {
self.audience = audience
}
}
class TragedyCalculator: PerformanceCalculator {
override var amount: Int {
var result = 40000
if audience > 30 {
result += 1000 * (audience - 30)
}
return result
}
}
class ComedyCalculator: PerformanceCalculator {
override var amount: Int {
var result = 30000
if audience > 20 {
result += 10000 + 500 * (audience - 20)
}
result += 300 * audience
return result
}
override var volumeCredits: Int {
return super.volumeCredits + audience / 5
}
}
func statement(invoice: Invoice, plays: Catalog) -> String {
return renderPlainText(data: StatementData(invoice: invoice, plays: plays))
}
func renderPlainText(data: StatementData) -> String {
var result = "Statement for \(data.customer)\n"
for performance in data.performances {
result += " \(performance.play.name): \(usd(performance.amount)) (\(performance.audience) seats)\n"
}
result += "Amount owed is \(usd(data.totalAmount))\n"
result += "You earned \(data.totalVolumeCredits) credits\n"
return result
}
func htmlStatement(invoice: Invoice, plays: Catalog) -> String {
return renderHTML(data: StatementData(invoice: invoice, plays: plays))
}
func renderHTML(data: StatementData) -> String {
var result = "<h1>Statement for \(data.customer)</h1>\n"
result += "<table>\n"
result += "<tr><th>play</th><th>seats</th><th>cost</th></tr>\n"
for performance in data.performances {
result += "<tr><td>\(performance.play.name)</td>"
result += "<td>\(performance.audience)</td>"
result += "<td>\(usd(performance.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
}
func usd(_ number: Int) -> String {
let format = NumberFormatter()
format.locale = Locale(identifier: "en-US")
format.numberStyle = .currency
return format.string(from: NSNumber(value: number/100)) ?? "N/A"
}
let plays: Catalog = [
"hamlet" : Play(name: "Hamlet", type: .tragedy),
"as-like" : Play(name: "As You Like It", type: .comedy),
"othello" : Play(name: "Othello", type: .tragedy)
]
let performances = [
Performance(playID: "hamlet", audience: 55),
Performance(playID: "as-like", audience: 35),
Performance(playID: "othello", audience: 40)
]
let invoice = Invoice(customer: "BigCo", performances: performances)
let text = statement(invoice: invoice, plays: plays)
print(text)
let html = htmlStatement(invoice: invoice, plays: plays)
print(html)
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