Typed segues on a per scene basis

[djbe]

SwiftGenKit PR: SwiftGen/SwiftGenKit#54

Uses the improvements added in SwiftGenKit to generate extensions for non-base classes (UIKit/AppKit), so that a user can:

• Perform a segue safely with an enum of segues that start from that scene (you can no longer incorrectly start a segue from a VC that doesn't support it).
• Prepare for a segue in a type safe way:
  • Have an exhaustive list of possible cases, including one for unnamed segues.
  • Get the segue's destination in the correct type (no need to cast it).
  • Get the segue itself as the correct subclass if you're using custom segues.

---

For performing a segue, the user goes from:

perform(segue: StoryboardSegue.MyStoryboard.nextStep)

To:

perform(segue: .nextStep)

For preparing for a segue, the user goes from:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let segueEnum = StoryboardSegue.MyStoryboard(segue: segue.identifier ?? "") {
        switch segueEnum {
        case .nextStep:
            guard let destination = segue.destination as? NextStepViewController else { return }
            // destination is casted version
        case .login:
            guard let destination = segue.destination as? LoginViewController else { return }
            // destination is casted version
        default:
            // Handle segues that are for other scenes
        }
    } else {
        // Handle unnamed segues
    }
}

To:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    switch TypedStoryboardSegue(segue: segue) {
    case .nextStep(let destination):
        // destination is casted version
    case .login(let destination):
        // destination is casted version
    case .unnamedSegue:
        // This case is added if you have unnamed segues (with identifier "")
    }
}

[djbe]

@AliSoftware proposed another idea, that we could add to this template (or an alternative one):

protocol MyViewControllerTypedStoryboardSegue {
  func prepareSegueForEmbed(destination: EmbedDestinationVC)
  func prepareSegueForModal(destination: ModalDestionationVC)
  …
  func prepare(for segue: NSStoryboardSegue, sender: Any?)
}
extension MyViewControllerTypedStoryboardSegue {
  func prepare(for segue: NSStoryboardSegue, sender: Any?) {
    /* generate that switch/case implementation here which calls the proper prepareSegueForXXX(destionation:) method */
  }
}

There could be issues here because of @objc dispatch and stuff, but could be interesting.

Another proposal was:

/* Generated by SwiftGen */
protocol MyViewControllerTypedStoryboardSegue {
  func prepareSegueForEmbed(destination: EmbedDestinationVC)
  func prepareSegueForModal(destination: ModalDestionationVC)
  …
  func prepare(for segue: NSStoryboardSegue)
}
extension MyViewControllerTypedStoryboardSegue {
  func prepare(for segue: NSStoryboardSegue) {
    /* generate that switch/case implementation here which calls
        the proper prepareSegueForXXX(destionation:) method */
  }
}

/* Added by the user */
extension MyViewController: MyViewControlelrTypedStoryboardSegue {
  @objc func prepare(for segue: NSStoryboardSegue, sender: Any?) {
    self.prepare(for: segue)
  }
}

I'd probably rename the function here, because users want access to the sender argument so we'd need to pass it along.

[djbe]

I'm going to wait on #36 to fix the last compilation issue (for the ignore-import case), as it needs the same per-file logic to add definitions.

[djbe]

Archiving this in favour of SwiftGen/SwiftGen#364.