Swift 4最全的新特性详细解析(推荐)

struct Date: Equatable, Comparable {
 private let secondsSinceReferenceDate: Double
 static func ==(lhs: Date, rhs: Date) -> Bool {
 return lhs.secondsSinceReferenceDate == rhs.secondsSinceReferenceDate
 }
 static func <(lhs: Date, rhs: Date) -> Bool {
 return lhs.secondsSinceReferenceDate < rhs.secondsSinceReferenceDate
 }
}

struct Date {
 private let secondsSinceReferenceDate: Double
}
extension Date: Equatable {
 static func ==(lhs: Date, rhs: Date) -> Bool {
 return lhs.secondsSinceReferenceDate == rhs.secondsSinceReferenceDate
 }
}
extension Date: Comparable {
 static func <(lhs: Date, rhs: Date) -> Bool {
 return lhs.secondsSinceReferenceDate < rhs.secondsSinceReferenceDate
 }
}

struct Date {
 fileprivate let secondsSinceReferenceDate: Double
}
...

protocol Shakeable {
 func shake()
}

extension UIButton: Shakeable { /* ... */ }
extension UISlider: Shakeable { /* ... */ }

func shakeEm(controls: [???]) {
 for control in controls where control.state.isEnabled {
 }
 control.shake()
}

func shakeEm(controls: [UIControl]) {
 for control in controls where control.isEnabled {
 if control is Shakeable {
  (control as! Shakeable).shake()
 }
 }
}

protocol Shakeable {
 func shake()
}

extension UIButton: Shakeable { /* ... */ }
extension UISlider: Shakeable { /* ... */ }

func shakeEm(controls: [UIControl & Shakeable]) {
 for control in controls where control.state.isEnabled {
 control.shake()
 }// Objective-C API
@interface NSCandidateListTouchBarItem<CandidateType> : NSTouchBarItem
@property (nullable, weak) NSView <NSTextInputClient> *client;
@end
}

// Objective-C API
@interface NSCandidateListTouchBarItem<CandidateType> : NSTouchBarItem
@property (nullable, weak) NSView <NSTextInputClient> *client;
@end

class NSCandidateListTouchBarItem<CandidateType: AnyObject> : NSTouchBarItem {
 var client: NSView?
}

class NSCandidateListTouchBarItem<CandidateType: AnyObject> : NSTouchBarItem {
 var client: (NSView & NSTextInputClient)?
}

associatedtype Element where <xxx>

protocol Sequence {
 associatedtype Element where Self.Element == Self.Iterator.Element
 // ...
}

@objcMembers class Kid: NSObject {
 dynamic var nickname: String = ""
 dynamic var age: Double = 0.0
 dynamic var friends: [Kid] = []
}

var ben = Kid(nickname: "Benji", age: 5.5)

let kidsNameKeyPath = #keyPath(Kid.nickname)

let name = ben.valueForKeyPath(kidsNameKeyPath)
ben.setValue("Ben", forKeyPath: kidsNameKeyPath)

\Kid.nickname

\.nickname

struct Kid {
 var nickname: String = ""
 var age: Double = 0.0
 var friends: [Kid] = []
}

var ben = Kid(nickname: "Benji", age: 8, friends: [])

let name = ben[keyPath: \Kid.nickname]
ben[keyPath: \Kid.nickname] = "BigBen"

struct GenericDictionary<Key: Hashable, Value> {
 private var data: [Key: Value]

 init(data: [Key: Value]) {
 self.data = data
 }

 subscript<T>(key: Key) -> T? {
 return data[key] as? T
 }
}

let dictionary = GenericDictionary(data: ["Name": "Xiaoming"])

let name: String? = dictionary["Name"] // 不需要再写 as? String

var family = "👩"
family += "\u{200D}👩"
family += "\u{200D}👧" 
family += "\u{200D}👦"

print(family)
print(family.characters.count)

let values = "one,two,three..."
var i = values.characters.startIndex

while let comma = values.characters[i...<values.characters.endIndex].index(of: ",") {
 if values.characters[i..<comma] == "two" {
 print("found it!")
 }
 i = values.characters.index(after: comma)
}

let values = "one,two,three..."
var i = values.startIndex

while let comma = values[i...<values.endIndex].index(of: ",") {
 if values[i..<comma] == "two" {
 print("found it!")
 }
 i = values.index(after: comma)
}

let values = "abcdefg"
let startSlicingIndex = values.index(values.startIndex, offsetBy: 3)
let subvalues = values[startSlicingIndex..<values.endIndex]
// defg

let values = "abcdefg"
let startSlicingIndex = values.index(values.startIndex, offsetBy: 3)
let subvalues = values[startSlicingIndex...] // One-sided Slicing
// defg

let abc: String = "abc"
print(String(abc.reversed()))
// cba

let abc: String = "abc"
for c in abc {
 print(c)
}
/*
a
b
c
*/

// map
let abc: String = "abc"
_ = abc.map {
 print($0.description)
}

// filter
let filtered = abc.filter { $0 == "b" }

// reduce
let result = abc.reduce("1") { (result, c) -> String in
 print(result)
 print(c)
 return result + String(c)
}
print(result)

let big = downloadHugeString()
let small = extractTinyString(from: big)

mainView.titleLabel.text = small // Swift 4 编译报错

mainView.titleLabel.text = String(small) // 编译通过

func tellJoke(name: String, character: Character) {
 let punchline = name.filter { $0 != character }
 let n = name.count - punchline.count
 let joke = "Q: Why does \(name) have \(n) \(character)'s in their name?\nA: I don't know, why does \(name) have \(n) \(character)'s in their name?\nQ: Because otherwise they'd be called \(punchline)."
 print(joke)
}
tellJoke(name: "Edward Woodward", character: "d")

func tellJoke(name: String, character: Character) {
 let punchline = name.filter { $0 != character }
 let n = name.count - punchline.count
 let joke = """
 Q: Why does \(name) have \(n) \(character)'s in their name?
 A: I don't know, why does \(name) have \(n) \(character)'s in their name?
 Q: Because otherwise they'd be called \(punchline).
 """
 print(joke)
}
tellJoke(name: "Edward Woodward", character: "d")

struct Language: Codable {
 var name: String
 var version: Int
}

let swift = Language(name: "Swift", version: 4)
if let encoded = try? JSONEncoder().encode(swift) {
 // 把 encoded 保存起来
}

if let decoded = try? JSONDecoder().decode(Language.self, from: encoded) {
 print(decoded.name)
}

protocol Sequence {
 associatedtype Iterator: IteratorProtocol
 func makeIterator() -> Iterator
}

protocol Sequence {
 associatedtype Element
 associatedtype Iterator: IteratorProtocol where Iterator.Element == Element
 func makeIterator() -> Iterator
}

protocol Sequence {
 associatedtype SubSequence: Sequence 
  where SubSequence.SubSequence == SubSequence,
    SubSequence.Element == Element
}

    +-------------+ +-------------+
  +------>+ Numeric | | Comparable |
  |  | (+,-,*) | | (==,<,>,...)|
  |  +------------++ +---+---------+
  |      ^  ^
+-------+------------+  |  |
| SignedNumeric |  +-+-------+-----------+
|  (unary -)  |  | BinaryInteger |
+------+-------------+  |(words,%,bitwise,...)|
  ^     ++---+-----+----------+
  |   +-----------^ ^  ^---------------+
  |   |    |      |
+------+---------++ +---------+---------------+ +--+----------------+
| SignedInteger | | FixedWidthInteger  | | UnsignedInteger |
|     | |(endianness,overflow,...)| |     |
+---------------+-+ +-+--------------------+--+ +-+-----------------+
    ^  ^     ^  ^
    |  |     |  |
    |  |     |  |
    ++--------+-+    +-+-------+-+
    |Int family |-+    |UInt family|-+
    +-----------+ |    +-----------+ |
     +-----------+    +-----------+

let n = NSNumber(value: 999)
let v = n as? UInt8 // Swift 4: nil, Swift 3: 231

var mutableArray = [1, 2, 3, 4]
mutableArray.swapAt(1, 2)
print(mutableArray)
// 打印结果：[1, 3, 2, 4]

struct Date {
 private let secondsSinceReferenceDate: Double
}

extension Date: Equatable {
 static func ==(lhs: Date, rhs: Date) -> Bool {
  return lhs.secondsSinceReferenceDate == rhs.secondsSinceReferenceDate
 }
}

extension Date: Comparable {
 static func <(lhs: Date, rhs: Date) -> Bool {
  return lhs.secondsSinceReferenceDate < rhs.secondsSinceReferenceDate
 }
}

class MyClass: NSObject {
 func print() { ... } // 包含隐式的 @objc
 func show() { ... } // 包含隐式的 @objc
}

extension MutableCollection {
 mutating func modifyEach(_ body: (inout Element) -> ()) {
  for index in self.indices {
   body(&self[index])
  }
 }
}

var numbers = [1, 2, 3]
numbers.modifyEach { element in
 element *= 2
 numbers.removeAll()
}