do something once

Once.swift

// http://www.fantageek.com/blog/2016/09/06/Once-in-Swift/

class Once {

  var already: Bool = false

  func run(@noescape block: () -> Void) {
    guard !already else { return }

    block()
    already = true
  }
}

class ViewController: UIViewController {
  let once = Once()

  override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)

    once.run {
      cameraMan.setup()
    }
  }
}