Migrating to Swift 4
Xcode 9 同时支持swift 4 和 swift 3.2，迁移方法：
Edit/Convert/To Current Swift Syntax…
API Changes
- Strings
- 集合类型
let galaxy = "Milky Way 🐮"
for char in galaxy {
print(char)
}
galaxy.count // 11
galaxy.isEmpty // false
galaxy.dropFirst() // "ilky Way 🐮"
String(galaxy.reversed()) // "🐮 yaW ykliM"
// Filter out any none ASCII characters
galaxy.filter { char in
let isASCII = char.unicodeScalars.reduce(true, { $0 && $1.isASCII })
return isASCII
} // "Milky Way "
- StringProtocol
// Grab a subsequence of String
let endIndex = galaxy.index(galaxy.startIndex, offsetBy: 3)
var milkSubstring = galaxy[galaxy.startIndex...endIndex] // "Milk"
type(of: milkSubstring) // Substring.Type
// Concatenate a String onto a Substring
milkSubstring += "🥛" // "Milk"
// Create a String from a Substring
let milkString = String(milkSubstring) // "Milk🥛"
- Dictionary and Set
- Sequence Based Initialization
let nearestStarNames = ["Proxima Centauri", "Alpha Centauri A", "Alpha Centauri B", "Barnard's Star", "Wolf 359"]
let nearestStarDistances = [4.24, 4.37, 4.37, 5.96, 7.78]
// Dictionary from sequence of keys-values
let starDistanceDict = Dictionary(uniqueKeysWithValues: zip(nearestStarNames, nearestStarDistances))
// ["Wolf 359": 7.78, "Alpha Centauri B": 4.37, "Proxima Centauri": 4.24, "Alpha Centauri A": 4.37, "Barnard's Star": 5.96]
- Duplicate Key Resolution
// Random vote of people's favorite stars
let favoriteStarVotes = ["Alpha Centauri A", "Wolf 359", "Alpha Centauri A", "Barnard's Star"]
// Merging keys with closure for conflicts
let mergedKeysAndValues = Dictionary(zip(favoriteStarVotes, repeatElement(1, count: favoriteStarVotes.count)), uniquingKeysWith: +) // ["Barnard's Star": 1, "Alpha Centauri A": 2, "Wolf 359": 1]
- Filtering
// Filtering results into dictionary rather than array of tuples
let closeStars = starDistanceDict.filter { $0.value < 5.0 }
closeStars // Dictionary: ["Proxima Centauri": 4.24, "Alpha Centauri A": 4.37, "Alpha Centauri B": 4.37]
- Dictionary Mapping
// Mapping values directly resulting in a dictionary
let mappedCloseStars = closeStars.mapValues { "\($0)" }
mappedCloseStars // ["Proxima Centauri": "4.24", "Alpha Centauri A": "4.37", "Alpha Centauri B": "4.37"]
- Dictionary Default Values
// Subscript with a default value
let siriusDistance = mappedCloseStars["Wolf 359", default: "unknown"] // "unknown"
// Subscript with a default value used for mutating
var starWordsCount: [String: Int] = [:]
for starName in nearestStarNames {
let numWords = starName.split(separator: " ").count
starWordsCount[starName, default: 0] += numWords // Amazing
}
starWordsCount // ["Wolf 359": 2, "Alpha Centauri B": 3, "Proxima Centauri": 2, "Alpha Centauri A": 3, "Barnard's Star": 2]
- Dictionary Grouping
// Grouping sequences by computed key
let starsByFirstLetter = Dictionary(grouping: nearestStarNames) { $0.first! }
// ["B": ["Barnard's Star"], "A": ["Alpha Centauri A", "Alpha Centauri B"], "W": ["Wolf 359"], "P": ["Proxima Centauri"]]
- Reserving Capacity（提高性能）
// Improved Set/Dictionary capacity reservation
starWordsCount.capacity // 6
starWordsCount.reserveCapacity(20) // reserves at _least_ 20 elements of capacity
starWordsCount.capacity // 24
- Private Access Modifier
struct SpaceCraft {
private let warpCode: String
init(warpCode: String) {
self.warpCode = warpCode
}
}
extension SpaceCraft {
func goToWarpSpeed(warpCode: String) {
if warpCode == self.warpCode { // Error in Swift 3 unless warpCode is fileprivate
print("Do it Scotty!")
}
}
}
let enterprise = SpaceCraft(warpCode: "KirkIsCool")
//enterprise.warpCode // error: 'warpCode' is inaccessible due to 'private' protection level
enterprise.goToWarpSpeed(warpCode: "KirkIsCool") // "Do it Scotty!"
API Additions
- Archival and Serialization
struct CuriosityLog: Codable {
enum Discovery: String, Codable {
case rock, water, martian
}
var sol: Int
var discoveries: [Discovery]
}
// Create a log entry for Mars sol 42
let logSol42 = CuriosityLog(sol: 42, discoveries: [.rock, .rock, .rock, .rock])
let jsonEncoder = JSONEncoder() // One currently available encoder
// Encode the data
let jsonData = try jsonEncoder.encode(logSol42)
// Create a String from the data
let jsonString = String(data: jsonData, encoding: .utf8) // "{"sol":42,"discoveries":["rock","rock","rock","rock"]}"
let jsonDecoder = JSONDecoder() // Pair decoder to JSONEncoder
// Attempt to decode the data to a CuriosityLog object
let decodedLog = try jsonDecoder.decode(CuriosityLog.self, from: jsonData)
decodedLog.sol // 42
decodedLog.discoveries // [rock, rock, rock, rock]
- Key-Value Coding
struct Lightsaber {
enum Color {
case blue, green, red
}
let color: Color
}
class ForceUser {
var name: String
var lightsaber: Lightsaber
var master: ForceUser?
init(name: String, lightsaber: Lightsaber, master: ForceUser? = nil) {
self.name = name
self.lightsaber = lightsaber
self.master = master
}
}
let sidious = ForceUser(name: "Darth Sidious", lightsaber: Lightsaber(color: .red))
let obiwan = ForceUser(name: "Obi-Wan Kenobi", lightsaber: Lightsaber(color: .blue))
let anakin = ForceUser(name: "Anakin Skywalker", lightsaber: Lightsaber(color: .blue), master: obiwan)
// Create reference to the ForceUser.name key path
let nameKeyPath = \ForceUser.name
// Access the value from key path on instance
let obiwanName = obiwan[keyPath: nameKeyPath] // "Obi-Wan Kenobi"
// Use keypath directly inline and to drill down to sub objects
let anakinSaberColor = anakin[keyPath: \ForceUser.lightsaber.color] // blue
// Access a property on the object returned by key path
let masterKeyPath = \ForceUser.master
let anakinMasterName = anakin[keyPath: masterKeyPath]?.name // "Obi-Wan Kenobi"
// Change Anakin to the dark side using key path as a setter
anakin[keyPath: masterKeyPath] = sidious
anakin.master?.name // Darth Sidious
// Note: not currently working, but works in some situations
// Append a key path to an existing path
//let masterNameKeyPath = masterKeyPath.appending(path: \ForceUser.name) �
//anakin[keyPath: masterKeyPath] // "Darth Sidious"
- Multi-line String Literals
let star = "⭐️"
let introString = """
A long time ago in a galaxy far,
far away....
You could write multi-lined strings
without "escaping" single quotes.
The indentation of the closing quotes
below deside where the text line
begins.
You can even dynamically add values
from properties: \(star)
"""
print(introString) // prints the string exactly as written above with the value of star
- One-Sided Ranges
// Collection Subscript
var planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
let outsideAsteroidBelt = planets[4...] // Before: planets[4..<planets.endIndex]
let firstThree = planets[..<4] // Before: planets[planets.startIndex..<4]
- Infinite Sequence
// Infinite range: 1...infinity
var numberedPlanets = Array(zip(1..., planets))
print(numberedPlanets) // [(1, "Mercury"), (2, "Venus"), ..., (8, "Neptune")]
planets.append("Pluto")
numberedPlanets = Array(zip(1..., planets))
print(numberedPlanets) // [(1, "Mercury"), (2, "Venus"), ..., (9, "Pluto")]
- Pattern Matching
// Pattern matching
func temperature(planetNumber: Int) {
switch planetNumber {
case ...2: // anything less than or equal to 2
print("Too hot")
case 4...: // anything greater than or equal to 4
print("Too cold")
default:
print("Justtttt right")
}
}
temperature(planetNumber: 3) // Earth
- Generic Subscripts
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
}
}
// Dictionary of type: [String: Any]
var earthData = GenericDictionary(data: ["name": "Earth", "population": 7500000000, "moons": 1])
// Automatically infers return type without "as? String"
let name: String? = earthData["name"]
// Automatically infers return type without "as? Int"
let population: Int? = earthData["population"]
extension GenericDictionary {
subscript<Keys: Sequence>(keys: Keys) -> [Value] where Keys.Iterator.Element == Key {
var values: [Value] = []
for key in keys {
if let value = data[key] {
values.append(value)
}
}
return values
}
}
// Array subscript value
let nameAndMoons = earthData[["moons", "name"]] // [1, "Earth"]
// Set subscript value
let nameAndMoons2 = earthData[Set(["moons", "name"])] // [1, "Earth"]
Miscellaneous
- MutableCollection.swapAt(::)
// Very basic bubble sort with an in-place swap
func bubbleSort<T: Comparable>(_ array: [T]) -> [T] {
var sortedArray = array
for i in 0..<sortedArray.count - 1 {
for j in 1..<sortedArray.count {
if sortedArray[j-1] > sortedArray[j] {
sortedArray.swapAt(j-1, j) // New MutableCollection method
}
}
}
return sortedArray
}
bubbleSort([4, 3, 2, 1, 0]) // [0, 1, 2, 3, 4]
- Associated Type Constraints
protocol MyProtocol {
associatedtype Element
associatedtype SubSequence : Sequence where SubSequence.Iterator.Element == Iterator.Element
}
- Class and Protocol Existential
protocol MyProtocol { }
class View { }
class ViewSubclass: View, MyProtocol { }
class MyClass {
var delegate: (View & MyProtocol)?
}
let myClass = MyClass()
//myClass.delegate = View() // error: cannot assign value of type 'View' to type '(View & MyProtocol)?'
myClass.delegate = ViewSubclass()
- NSNumber Bridging
let n = NSNumber(value: 999)
let v = n as? UInt8 // Swift 4: nil, Swift 3: 231
