bug.swift

// This code has a bug. When you try to make a change to the selection
// it will not persist. The `selection` binding is never written to
// no matter what you do in the UI.

import SwiftUI

struct TestView: View {
  @State var selection: Int?

  var body: some View {
    NavigationView {
      Form {
        Picker(selection: self.$selection, label: Text("Pick")) {
          Text("None")
            .tag(Int?.none)

          ForEach(0...10, id: \.self) { int in
            Text("\(int)")
              .tag(int)
          }
        }
      }
    }
  }
}

import PlaygroundSupport
PlaygroundPage.current.setLiveView(TestView())

fix.diff

// This fixes the bug described above
 
 import SwiftUI
 
 struct TestView: View {
   @State var selection: Int?
 
   var body: some View {
     NavigationView {
       Form {
         Picker(selection: self.$selection, label: Text("Pick")) {
           Text("None")
             .tag(Int?.none)
 
           ForEach(0...10, id: \.self) { int in
             Text("\(int)")
-              .tag(int)
+              .tag(Optional(int))
           }
         }
       }
     }
   }
 }
 
 import PlaygroundSupport
 PlaygroundPage.current.setLiveView(TestView()) 

I think another option is that on line 15, explicitly define the parameter as an optional Int:

ForEach(0...10, id: \.self) { (int: Int?) in

@pcolton interesting! thanks for sharing that. that's good to know.