import SwiftUI

struct ImplicitDemo: View {
  @State private var on = false
  var body: some View {
    Circle()
      .fill(on ? .green : .gray)
      .frame(width: on ? 120 : 60, height: on ? 120 : 60)
      .animation(.spring(), value: on)
      .onTapGesture { on.toggle() }
  }
}

                    

import SwiftUI

struct ContentView: View {
  var body: some View {
    ImplicitDemo()
  }
}

                    

import SwiftUI

@main
struct MyApp: App {
  var body: some Scene {
    WindowGroup { ContentView() }
  }
}