[Swift]enumでランダムなケースを返すextension

実装

public protocol Sampling {
  static var all: [Self] { get }
  static var sample: Self? { get }
}

public extension Sampling {
  static var sample: Self? {
    let all = self.all
    if all.isEmpty { return nil }
    let index = Int(arc4random_uniform(UInt32(all.count)))
    return all[index]
  }
}

extension Sampling where Self: CaseIterable {
  static var all: [Self] { return self.allCases as! [Self] }
}

使い方

enum Basic {
  case one
  case two
}

enum IteratableBasic: CaseIterable {
  case one
  case two
}

enum Nums: Int {
  case zero
  case one
}

enum IteratableNums: Int, CaseIterable {
  case zero
  case one
}

enum Args {
  case str(String)
  case num(Int)
}

extension Basic: Sampling {
  static var all: [Basic] { return [.one, .two] }
}
extension IteratableBasic: Sampling {}
extension Nums: Sampling {
  static var all: [Nums] { return [.one, .zero] }
}
extension IteratableNums: Sampling {}
extension Args: Sampling {
  static var all: [Args] { return [.num(123), .str("mes")] }
}

Basic.sample
IteratableBasic.sample
Nums.sample
IteratableNums.sample
Args.sample