Constant bindings as placeholders

⇐ Notes archive

(This is an entry in my technical notebook. There will likely be typos, mistakes, or wider logical leaps — the intent here is to “let others look over my shoulder while I figure things out.”)

When building layouts in SwiftUI, I’ll often sketch out the views — ignoring data flow — and then turn my attention towards state management. However, since many view initializers require bindings (e.g. TextField.init or Toggle.init), that puts things in an awkward spot.

What do I slot in if I haven’t determined whether to back the view with @State, @ObservedObject, another @Binding, TCA-backed state, or the like?

Is there a placeholder I can use in the same way fatalError appeases the compiler while I think through an implementation?1

Brandon and Stephen showed a technique early in episode #131 (timestamped).

For now, we’ll use a constant binding because we don’t have anywhere to send the user’s changes, but we will get to that soon.

Aha! That’s a solid trick — here’s a Toggle example with its binding fixed to false.

import SwiftUI

struct SampleView: View {
  var body: some View {
    Toggle("A toggle", isOn: .constant(false))

  1. Never as a universal “bottom” subtype was unfortunately not pursued in SE-0102.