AdvancesInFoundation.md

Advances in Foundation

@ WWDC 19

Ordered Collection Diffing

[B, E, A, R] 에서 [B, I, R, D] 를 만드려면

1. 공통되는 요소를 찾는다. [B, R]
2. [B, E, A, R]에서 공통되지 않는 요소 제거 -> [B, R]
3. [B, I, R, D]로 만들기 위해 필요한 요소 삽입 -> [B, R] -> [B, I, R, D]

let diff = bird.difference(from: bear)
let newBird = bear.applying(diff)

Data

Contiguity

Data는 연속적임이 보장된다.

public protocol ContiguousBytes {
  func withUnsafeBytes<R>(_ body: (UnsafeRawBufferPointer) throws -> R) rethrows -
  > R
}

ContiguousBytes 프로토콜을 채택함으로써 차후 flattening을 걱정할 필요가 없어진다.

public protocol DataProtocol: RandomAccessCollecton where Element == UInt8, ... { }

public protocol MutableDataProtocol: DataProtocol, MutableCollection, RangeReplaceableCollection { }

연속성을 보장하지 않는 다른 버퍼 타입에 대해서는 채택할 수 있는 두 개의 프로토콜을 소개한다.

Compression

let compressed = try data.compressed(using .lzfse)

public enum CompressionAlgorithm: Int {
  case lzfse
  case lz4
  case lzma
  case zlib
}

데이터 압축은 위와 같은 api를 이용해서 쉽게 처리 가능하다.

Units

• UnitDuration

  • Added milliseconds, microseconds, nanoseconds, and picoseconds

• UnitFrequency

  • Added framePerSecond

• UnitInformationStorage

  • bits, bytes, nibbles for common usage
  • SI- and binary-prefixed units (kilo, kibi, ..., yotta, yobi)
  • Format with MeasurementFormatter and ByteCountFormatter

Relative Date Formatter

let formatter = RelativeDateTimeFormatter()
let dateString = formatter.localizedString(for: aDate, relativeTo: now)

List Formatter

let string = ListFormatter.localizedString(byJoining: ["🐶", "🐷", "🦄"])

let listFormatter = ListFormatter()
let dateFormatter = DateFormatter()

listFormatter.itemFormatter = dateFormatter
let string = listFormatter.string(from: dates)

// en_US: "8/15/19, 9/13/19, and 2/1/20"
// en_ES: "15/8/19, 13/9/19 y 1/2/20"

let listFormatter = ListFormatter()
let dateFormatter = DateFormatter()
dateFormatter.dateStyle = .medium

listFormatter.itemFormatter = dateFormatter
let string = listFormatter.string(from: dates)

Operation Queue

모든 작업이 끝나고 난 다음 저장을 하고 싶다면

// 잘못된 예시
if (queue.operationCount == 0) {
  save()
}
// 잘 작동하는 예시
queue.addBarrierBlock {
  save()
}

이 경우 미리 스케쥴 된 작업들이 완료되고 난 후 save()가 실행됨을 보장한다.

Progress reporting

let queue = OperationQueue()
queue.progress.totalUnitCount = 3

queue.addOperation {
  task1()									// Finished task: 1 / 3
}

queue.addOperation {
  task2()									// Finished task: 2 / 3
}

queue.addOperation {
  task3()									// Finished task: 3 / 3
}

Be Prepared for USB and SMB on iOS

• Multiple volumes
  • Use FileManager.SearchPathDirectory.itemReplacementDirectory
• Disappearing volumes
  • Use Data.ReadingOptions.mappedIfSafe
• Slower file system operations
  • Defer access to non-main thread
• Varying capabilities
  • Test capabilites with URLResourceKey, e.g. volumeSupportsFileCloningKey
  • Handle errors

Swift Update

Scanner

// Swift 4
var nameNSString: NSString?
if scanner.scanUpToCharacters(from: .newlines, into: &nameNSString) {
  let name = nameNSString! as String
}

// Swift 5.1
let nameString = scanner.scanUpToCharacters(from: .newlines)
let matchedString = scanner.scanString(string: "hi, 👩‍💻") // emoji 가능

FileHandle

• Error-based API

  let fileHandle = FileHandle()
  let data = try fileHandle.readToEnd()

• Works with DataProtocol

  extension FileHandle {
    public func write<T: DataProtocol>(contentsOf data: T) throws
  }

Try It

• Use DataProtocol instead of [UInt8]
• Format dates and lists with Formatter
• Use OperationQueue's barrier and progress reporting