why is error in swiftUI body?
Code Block swift struct ContentView: View { @Converter("100", from: "USD", to: "CNY", rate: 6.78) var usd_cny var body: some View { VStack(alignment: .leading, spacing: 10) { Button(action: { update("200") }) { Text(self.$usd_cny) } } } mutating func update(_ price: String) { self.usd_cny = price } } @propertyWrapper struct Converter { var from: String var to: String var rate: Double var value: Double var wrappedValue: String { get { "\(from)\(value)"} set { value = Double(newValue) ?? -1} } var projectedValue: String { return "\(to)\(value * rate)" } init(_ value: String, from: String, to: String, rate: Double) { self.rate = rate self.value = 0 self.from = from self.to = to self.wrappedValue = value } mutating func update(_ value: String) { self.wrappedValue = value } } struct ContentView_Previews: PreviewProvider { static var previews: some View { ContentView() } }