How to organize swift source code in pattern? - ios

Question

I have some codes in java which organized well, so it helps me manage source code as well as extend in future easily. These codes as follow
public interface IDataModel<T extends IDataModel> {
void copyData(T data);
long getUpdatedTime();
}
public abstract class AbstractDataModel<T extends IDataModel> implements IDataModel<T>{
protected long updatedTime;
public long getUpdatedTime(){
return updatedTime;
}
}
public class concreteDataA extends AbstractDataModel<concreteDataA>{
String property1;
public String getProperty1(){
return property1;
}
#override
public void copyData(concreteDataA data){
property1 = data.getProperty1();
updatedTime = data.getUpdatedTime();
}
}
Now i want to port into iOS swift 3.0. Is it possible to organize code in swift 3.0 as above? Or is there any equivalent way in swift to organize code as above? I'm quite new to swift iOS, so it makes me hard to organize source code in pattern. Thanks you.

Answer 1

You haven't provided much in the way of context, but it seems like you're struggling developing a "protocol-oriented" solution, as Swift folks like to call the pattern. Here are a couple of options that might solve your problem (spoiler – I think the problem is in your design):
Interface: Protocol, Abstract Class: Protocol Extension
Like #sulthan mentioned, you can certainly get to a similar place using protocols with default implementations, like so:
protocol DataModel {
mutating func copy(data: Self)
var updatedTime : Float { get }
}
extension DataModel {
var updatedTime : Float { return 0 }
}
However, you'll run into a problem when you try to implement the ConcreteDataModel since you want to specialize it to account for the property1 value that isn't mentioned in the protocol. Your options are to relax that requirement in ConcreteDataModel (aka don't do that) or use typecasting. Please note, fighting the typing system in Swift is a sure sign that your code is not idiomatic! You should see this difficulty as the language nudging you to reconsider your approach.
Use immutable data types
This is the most straight-forward answer. If what you've described above is actually a concrete example from your app, then you don't really need protocols at all. (In fact, your Java implementation is certainly over-abstracting.) Swift structs are immutable, which means that whenever you change them, you are actually changing a copy.
struct DataModel {
let updatedTime: Float
mutating func update(time: Float) {
self = DataModel(updatedTime: time)
}
}
var data1 = DataModel(updatedTime: 3)
var data2 = data1
data2.update(time: 17)
print(data1.updatedTime) // 3.0
print(data2.updatedTime) // 17.0
Model your behavior apart from your data
This is the generalized solution. From a design perspective, it's clear that you have two distinct concerns. You want something copyable, and you want something that tracks "time." Why not just let your code reflect that?
protocol Copier {
associatedtype Data
func copy(from: Data) -> Data
}
protocol Clock {
var time: Float { get }
}
class AlarmClock: Clock, Copier {
let time: Float
let alarm: Float
init(time: Float, alarm: Float) {
self.time = time
self.alarm = alarm
}
func copy(from: AlarmClock) -> AlarmClock {
return AlarmClock(time: from.time, alarm: from.alarm)
}
}
Of course, you could even go the last step and provide the default implementation for Clock.time if you really needed it.