Optional chaining raw value conversion

String2Enum.swift

extension String {
  func toEnum<Enum: RawRepresentable where Enum.RawValue == String>() -> Enum? {
    return Enum(rawValue: self)
  }
}

enum Segue: String {
  case Foo
  case Bar
}

let x: String = "Foo"
let y: Segue? = x.toEnum()