hello.swift

struct ContentView: View {
    @State var prop: Bool = true
    var body: some View {
        VStack {
            Rectangle()
            .fill(prop ? Color.red : Color.green)
            .frame(width: prop ? 100 : 300, height: prop ? 50 : 200)
                .animation(.linear)
            Spacer()
            Toggle(isOn: $prop, label: { Text("Toggle") })
        }
    }
}