Swift in Practice

(WWDC15-411)

Compatibility checking

• Always use the Latest SDK
• Toggle deployment target back to earliest release
• Need to check absence of:
  • frameworks (mark as optional if unavailable on earlier OS)
  • classes/method
    • what if the class/method is private/pre-release?
  • enums (stuck with doing a manual OS version check)
• In Swift:
  • compiler emits error if API is unsafely used
  • with modules, optional linking is automatic
  • unified syntax for compatibility checks
    • #available(iOS 8.0. *)
    • compiler generates runtime check, infers min OS version
• Use guard to bail out early
  • guard #available(iOS 9.0, OSX 10.11, *) else { return }
• Use @available(iOS 8.0, *) to annotate methods

Use nested type enums instead of string constants

• Strongly-typed > Stringly-typed
• Centrally located constants
• Doesn't pollute global namespace
• Compiler enforces uniqueness of enum cases
• Allows APIs to be non-failable

extension UIImage {
  enum AssetIdentifier: String {
    case Isabella = "Isabella"
    case William = "William"
  }
  
  convenience init(assetIdentifier: AssetIdentifier) { ... }
}

let image = UIImage(assetIdentifier: .Isabella)

Constrained protocol extensions

protocol SegueHandlerType {
  typealias SegueIdentifier: RawRepresentable
}

extension SegueHandlerType where Self: UIViewController, 
  SegueIdentifier.RawValue == String {

  func performSegueWithIdentifier(...){...}
}

class BrowserViewController: UIViewController, SegueHandlerType {
  // satisfies typealias constraint of protocol
  enum SegueIdentifier: String { 
    ...
  }
}