Swift `switch()` and `next()` extension for enums

CaseSwitchable.swift

protocol CaseSwitchable: CaseIterable, Equatable {}

extension CaseSwitchable {
  mutating func `switch`() {
    self = next()
  }

  func next() -> Self {
    self.next() ?? Self.allCases.first!
  }

  func next() -> Self? {
    let index = Self.allCases.firstIndex(of: self)!
    let nextIndex = Self.allCases.index(after: index)
    guard nextIndex < Self.allCases.endIndex else {
      return nil
    }
    return Self.allCases[nextIndex]
  }
}

// MARK: - Example

enum MyEnum: CaseSwitchable {
  case one
  case two
  case three
}

var value = MyEnum.one

value.switch() // → two
value.switch() // → three
value.switch() // → one

let next1: MyEnum = value.next() // → two
let next2: MyEnum = next1.next() // → three
let next3: MyEnum = next2.next() // → one

let optionalNext1: MyEnum? = value.next() // → two
let optionalNext2: MyEnum? = next1.next() // → three
let optionalNext3: MyEnum? = next2.next() // → nil