New to Swift and am trying to use structs where I can hold values. When I try to bind them with a TextField it doesn't update the actual variable. What is wrong?           @State var final = finalBluePrint()       var body : some View {           NavigationView {                        VStack {                       TextField("Current Grade", value: $final.currentGrade, format: .number).keyboardType(.decimalPad);                       TextField("Desired Grade", value: $final.desiredGrade, format: .number).keyboardType(.decimalPad);                                   TextField("Final Weight", value: $final.finalWeight, format: .number).keyboardType(.decimalPad);                                   Text(final.currentGrade, format: .number);                                               Text(final.finalNeededGrade, format: .number);         }       @State var currentGrade: Double = 5;   @State var desiredGrade : Double = 0;   @State var finalWeight : Double = 0;                   var finalNeededGrade : Double {           let desiredGrade = self.desiredGrade;     let currentGrade = self.currentGrade;     let finalWeight = self.finalWeight;           let finalNeededGrade = (desiredGrade - currentGrade * (100 - finalWeight)) / finalWeight;           return finalNeededGrade         }     Thank you!