Styjun

I am Swift newcomer from C#. I started designing the Swift program from the abstract level - declaring entities signatures with relationships between them. I caught that protocol in swift is analog of the interface in C# or Java. From my (as Swift newcomer from C#) point of view, generics in protocols implemented in Swift by an uncommon way. I researched about associated types but continuously didn't know how to do the following:

typealias Observer<T> = (T) -> ()

protocol Subscription 
 func cancel()


protocol Observable<T> 
 func subscribe(observer: Observer<T>) -> Subscription


protocol A 
protocol B 
protocol C 

protocol AbcObservable 
 var aAdded : Observable<A> get 
 var bAdded : Observable<B> get 
 var cAdded : Observable<C> get 

The code above is from the imaginary world where generic protocols have the same struct as generic classes. Is it possible to write the code above compilable by associated types using? How? If it is impossible, what is an alternative?

Remark 1

I need described architecture to provide something like the following:

class First: AbcObservable ... 
class Second: AbcObservable ... 

class Client 
 let lightDependency: AbcObservable
 init(lightDependency: AbcObservable) 
 self.lightDependency = lightDependency
 


class IoCContainer1 
 let client: Client
 init() 
 let abc: AbcObservable = First()
 client = Client(abc)
 


class IoCContainer2 
 let client: Client
 init() 
 let abc: AbcObservable = Second()
 client = Client(abc)
 


class Mock: AbcObservable ... 

class Test 
 func test() 
 let abcMock = Mock()
 let client = Client(abcMock)
 ...
 

This moment is very painfully for me; I can't understand how I can provide D of SOLID in my code in the case when I need generics.

Remark 2

Observable will not have many implementations in the real situation and it is stupid to do it as abstract. I wanted to write the essence of my problem, and I used Observable in the example to simplify. In a real situation, I had DataManager instead of Observable, that has many implementations.

Remark 3

The question was changed from "How to use protocol with associatedtype in another protocol?" to "What is equivalent for C# or Java generic interface in Swift?"

You've overused protocols here, but this is the syntax you'd want. Several of these pieces can't reasonably be protocols. I have trouble imagining three different implementations of Observable, and certainly not of Subscription. (If you can't imagine three implementations, it's probably not a protocol.) Trying to make Observable into a protocol definitely causes the whole thing to explode.

Subscription is just a wrapper around a function, so that's struct. Observable is naturally a class. The rest is possibly fine; your problems there are mostly syntax.

import Foundation

typealias Observer<T> = (T) -> ()

struct Subscription 
 let cancel: () -> Void


final class Observable<T> 
 private var observations: [UUID: Observer<T>] = [:]
 func subscribe(observer: @escaping Observer<T>) -> Subscription 
 let uuid = UUID()
 observations[uuid] = observer
 return Subscription(cancel: [weak self] in self?.observations[uuid] = nil )
 


protocol A 
protocol B 
protocol C 

protocol AbcObservable 
 var aAdded : Observable<A> get 
 var bAdded : Observable<B> get 
 var cAdded : Observable<C> get 


struct First: AbcObservable 
 let aAdded = Observable<A>()
 let bAdded = Observable<B>()
 let cAdded = Observable<C>()


struct Second: AbcObservable 
 let aAdded = Observable<A>()
 let bAdded = Observable<B>()
 let cAdded = Observable<C>()


struct Client 
 let lightDependency: AbcObservable
 init(lightDependency: AbcObservable) 
 self.lightDependency = lightDependency
 


struct IoCContainer1 
 let client: Client
 init() 
 let abc: AbcObservable = First()
 client = Client(lightDependency: abc)
 


class IoCContainer2 
 let client: Client
 init() 
 let abc: AbcObservable = Second()
 client = Client(lightDependency: abc)
 


struct Mock: AbcObservable 
 let aAdded = Observable<A>()
 let bAdded = Observable<B>()
 let cAdded = Observable<C>()


class Test 
 func test() 
 let abcMock = Mock()
 let client = Client(lightDependency: abcMock)
 

The Observer implementation here is based on my Subject implementation. Note that this is part of a system that has several quirks that I don't love (Dave Delong's Syzygy is better).