iOS version available (target iOS devices lower than a specific OS)

Available.swift

typealias iOS = OperatingSystemVersion

extension OperatingSystemVersion {
  init(_ major: Int) {
    self.init(majorVersion: major, minorVersion: 0, patchVersion: 0)
  }
}

extension OperatingSystemVersion: Comparable {
  public static func < (lhs: OperatingSystemVersion, rhs: OperatingSystemVersion) -> Bool {
    guard lhs.majorVersion == rhs.majorVersion else {
      return lhs.majorVersion < rhs.majorVersion
    }

    guard lhs.minorVersion == rhs.minorVersion else {
      return lhs.minorVersion < rhs.minorVersion
    }

    return lhs.patchVersion < rhs.patchVersion
  }

  public static func == (lhs: OperatingSystemVersion, rhs: OperatingSystemVersion) -> Bool {
    return lhs.majorVersion == rhs.majorVersion &&
           lhs.minorVersion == rhs.minorVersion &&
           lhs.patchVersion == rhs.patchVersion
  }
}

func available(_ version: OperatingSystemVersion, _ compare: (OperatingSystemVersion, OperatingSystemVersion) -> Bool) -> Bool {
  return compare(ProcessInfo.processInfo.operatingSystemVersion, version)
}


// usage:
if available(iOS(11), <) {
  print("not ios 11")
} else {
  print("ios 11")
}