CaseIterable non-optional index

CaseIterableIndex.swift

enum NoteLetter: CaseIterable {
  case c
  case d
  case e
  case f
  case g
  case a
  case b
}

extension CaseIterable where Self: Equatable {
  static var count: Int {
    return Self.allCases.count
  }

  static func index(of item: Self) -> AllCases.Index {
    return allCases.firstIndex(of: item)!
  }

  static func element(atIndex index: AllCases.Index) -> Self {
    return allCases[index]
  }
}

NoteLetter.element(atIndex: 3) // NoteLetter.f
NoteLetter.count // 7
NoteLetter.index(of: .a) // 5