1. The document discusses several software design principles and best practices including SOLID principles, optional binding, lazy evaluation, and type casting. 2. It provides examples of applying single responsibility principle (SRP), dependency inversion principle (DIP), and interface segregation principle (ISP) to code. 3. Guidelines are also given for naming conventions, computed properties versus methods, and value types versus reference types.

1. twitter.com/@godrm
facebook.com/godrm

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4. ✱ Main - , , ,
✱ Reusability - DRY, components, generics
✱ Reliability - Exception handling and cleanup
✱ Extensibility
✱ Security - , , ,
✱ Performance - , Lazy Loading, ,
✱ Scalability -
✱ Usability -

5. - SOLID
1. SRP (Single-Responsibility Principle)
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2. OCP (Open-Close Principle)
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3. LSP (Liskov Substitution Principle)
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4. DIP (Dependency-Inversion Principle)
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5. ISP (Interface-Segregation Principle)
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6. SRP
struct InputView {
func readInput() {
print(" .")
let userCoordinate = readLine()
guard let input = userCoordinate else { return }
print(seperateCoordinates(userInput: input))
}
//…
}
struct InputView {
func readInput() -> String {
print(" .")
let userCoordinate = readLine()
guard let input = userCoordinate else { return "" }
return input
}
//…
}

7. DI
class MessageListViewController: UITableViewController {
private let loader: MessageLoader
init(loader: MessageLoader) {
self.loader = loader
super.init(nibName: nil, bundle: nil)
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
loader.load { [weak self] messages in
self?.reloadTableView(with: messages)
}
}
}
✱
✱
✱

8. Interface Protocol Segregation
protocol MyShape {
var resultDescription: String { get }
func calculateOfPosition() -> [MyPoint]
func resultOfMyShape() -> Double
}
struct MyLine: MyShape {
private(set) var pointA = MyPoint()
private(set) var pointB = MyPoint()
func calculateOfPosition() -> [MyPoint] { return [pointA, pointB] }
func resultOfMyShape() -> Double { return calculateOfLength() }
//
var resultDescription: String = {
return " "
}()
}
struct MyPoint: MyShape {
private(set) var x = 0
private(set) var y = 0
func calculateOfPosition() -> [MyPoint] { return [self] }
func resultOfMyShape() -> Double { return 0 }
var resultDescription: String = { return "" }()
}
(before)

9. Protocol Segregation (after)
protocol MyShape {
func calculateOfPosition() -> [MyPoint]
func resultOfMyShape() -> Double
}
protocol MyDescription {
var resultDescription: String { get }
}
struct MyLine: MyShape, MyDescription {
private(set) var pointA = MyPoint()
private(set) var pointB = MyPoint()
func calculateOfPosition() -> [MyPoint] { return [pointA, pointB] }
func resultOfMyShape() -> Double { return calculateOfLength() }
var resultDescription: String = {
return " "
}()
}
struct MyPoint: MyShape {
private(set) var x = 0
private(set) var y = 0
func calculateOfPosition() -> [MyPoint] { return [self] }
func resultOfMyShape() -> Double { return 0 }
}

10. Optional
guard let y = x { ... }
//
let image = UIImage(named: "Background") if image == nil {
print("Image not loaded ")
return
}
let size = image!.frame.size.scaled(by: 2.0)
//
let image = UIImage(named: selectedImageName)!
guard let x = x { ... }
//
guard let image = image else {
print("Image not loaded"); return
}
let size = image.size.scaled(by: 2.0)
//
guard let image = UIImage(named: selectedImageName)
else { preconditionFailure("Missing (selectedImageName)
asset") }

11. IUO
class Company {
let name: String
var ceo: CEO!
init(name: String, ceoName: String) {
self.name = name
self.ceo = CEO(name: ceoName, company: self)
}
}
class CEO {
let name: String
unowned let company: Company
init(name: String, company: Company) {
self.name = name
self.company = company
}
}
let company = Company(name: "HK", ceoName: "Min")

12. Enum Associated Value
enum JSONData {
case null
case bool(Bool)
case number(Double)
case string(String)
case array([JSONData])
case object([String: JSONData])
var string: String? {
guard case .string(let s) = self else { return nil }
return s
}
var array: [JSONData]? {
guard case .array(let a) = self else { return nil }
return a
}
var object: [String: JSONData]? {
guard case .object(let o) = self else { return nil }
return o
}
}
case bool(boolValue: Bool)
case number(numberValue: Double)X

13. Enum Error
enum Error: String, Error {
case invalidFormat = " ."
case quit = " ."
case notFound = " ."
}
enum MenuError: Error {
case invalidFormat
case quit
case notFound
var localizedDescription: String {
switch self {
case .invalidInput:
return " ."
case .quit:
return " ."
case .notFound:
return " ."
}
}
}
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14. Type Casting conditionally
var dict: [AnyHashable: Any] = [:]
dict["age"] = 33
if let anyValue = dict[“age"],
anyValue is Int
{
let intValue = anyValue as! Int
//
}
guard let intValue = dict[“age"] as? Int else { return }
let wrappedValue: AnyHashable? = "value" // typed AnyHashable?
let unwrappedValue: AnyHashable = "value" // typed AnyHashable
let optString1 = unwrappedValue as? String // typed String?
let optString2 = wrappedValue as? String // typed String?
let veryOptyString: String???????????? = optString2 // Typed String????????????
let lessOptyString: String??? = veryOptyString // Error!

15. Lazy Eveluation
internal init(_ seq1: Sequence1, _ seq2: Sequence2)
let sequence = seq1.lazy.flatMap ({
item1 in seq2.lazy.map ({
item2 in (item1, item2)
})
})
_iterator = sequence.makeIterator()
}
✱
✱ (Eager)
✱ lazily, eagerly

16. guard vs if-else
static func analyzeJSONData(in value: String) throws -> JSONDataCountable {
if value.isEmpty {
throw JSONError.emptyValue
}
guard value.hasPrefix(JSONDataTypePattern.leftBrace) else {
return try makeJSONArray(in: value)
}
return try makeJSONObject(in: value)
}
static func analyzeJSONData(in value: String) throws -> JSONDataCountable {
guard value.count > 0 else {
throw JSONError.emptyValue
}
if value.hasPrefix(JSONDataTypePattern.leftBrace) {
//
return try makeJSONObject(in: value)
}
return try makeJSONArray(in: value)
}

17. Trailing Closures
let words = sentence.characters.split(separator: " ")
.filter({ $0.count > 4 })
.map({ String($0) })
let nums: [Int] = arguments
.flatMap({ Int($0, radix:10) })
.flatMap({ $0 > 0 ? $0 : nil })
dispatch(after: maxItem + 1) { semaphore.signal() }
DispatchQueue
.global(qos: .default) .asyncAfter(deadline: delay) {
// ...
}
UIView.animate(withDuration: 0.3) {
// ...
}
for value in items.map({ pow($0, 2) }) {
print(value)
}
//
UIView.animate(withDuration: 2.0,
animations: { v.removeFromSuperview() },
completion: { _ in postNotification() } )

18. ?
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아냐 너 먼저가...아마.. 쉬울꺼야

19. Best Practices & Styles
✱ Tab vs. Space
✱ Braces Styles
✱ Variable, Function, Class - Naming Rules
✱ Computed Properties vs. Methods
✱ Protocol + Extension + Generic
✱ Value Types vs. Reference Types

20. 1. (intent) .
2. else .
3. .
4. .
5. ( )
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7. 2 .
8. .
9. / / .

22. 
Software maintenance is
not 'keep it working like before'.
It is 'keep it being useful in a changing world’
- Jessica Kerr