Swift Generics and Protocols Not Working on Uikit [Possible Bug]

Swift Generics and Protocols not working on UIKit [possible bug]

That's correct behavior from the documentation point of view, because:

Method in a generic class cannot be represented in Objective-C

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Reply to @Bell App Lab comment:

Open this page and scroll down to Lightweight Generics. Here's note:

Aside from than these Foundation collection classes, Objective-C
lightweight generics are ignored by Swift. Any other types using
lightweight generics are imported into Swift as if they were
unparameterized.

It basically says that generics (ObjC -> Swift) are imported only for Foundation collection classes and rest is ignored - IOW imported as if they are unparameterized.

Maybe we can expect some improvement in this area in the future, but I doubt it.

Swift Generics and Protocol Extensions

That's an interesting problem. Your code seems like it should work; you might want to file an enhancement request.

Here's a workaround that seems to work correctly:

class SomeGenericClass<CellType: Cell> {
    func someFunction() {
        let reuseIdentifier = (CellType.self as Reusable.Type).reuseId()
    }
}

EXC_BAD_ACCESS when creating an object with Generics, Protocols and Inheritance in Swift

Update Swift 1.2 XCode 6.3 Beta 2 (Beta 1 will not work):
Your code now runs without any problems and the expected result:

var b = creation(x: B.self); //{__lldb_expr_9.SecondBase}
var a = creation(x: A.self); //{__lldb_expr_11.FirstBase}

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They conflict because FirstBase has no init but EmptyInit a required init.
This way it will work:

protocol EmptyInit {
    init();
}

class FirstBase {
    required init(){

    }
}

class SecondBase : EmptyInit {
    required init(){

    }
}

class A : FirstBase, EmptyInit{
    required init(){

    }
}

class B : SecondBase, EmptyInit {
    required init() {

    }
}

A();
B();

func creation<T: EmptyInit>(x a:T.Type) -> T{
    var object = T()
    return object;
}

var b = creation(x: B.self); // SecondBase
var a = creation(x: A.self); // FirstBase

Is it possible to pass generic protocols into a constructor for proper Dependency Injection in Swift 3?

The answer to your question is yes it is definitely possible, just that it currently requires some PAT-related "magic". With Swift3 and Xcode 8.0 beta 4, you should be able to run the following in a playground:

protocol Persistable {
    var id: Int { get set }
}
protocol RepositoryProtocol: class {
    associatedtype Object: Persistable
    func insert(_ object: Object) -> Void
    func deleteAll()
}
protocol ZombieServiceProtocol {
    associatedtype RepositoryType: RepositoryProtocol
    var zombieRepository: RepositoryType { get set }
    func fetchZombies()
}
public struct Zombie: Persistable {
    var id: Int
    let name: String?
}

// Mocks
class RepositoryMock<Object: Persistable>: RepositoryProtocol {
    func insert(_ object: Object) { print("look, there's another one!")}
    func deleteAll() { print("it's safe out there, all zombies have been deleted") }
}
struct ZombieServiceMock<RepositoryType: RepositoryProtocol
                    where RepositoryType.Object == Zombie>: ZombieServiceProtocol {
    var zombieRepository: RepositoryType
    init(zombieRepository: RepositoryType) {
        self.zombieRepository = zombieRepository
    }
    func fetchZombies() {
        self.zombieRepository.deleteAll()
        self.createMockZombies()
    }
    private func createMockZombies() {
        for index in 1...5 {
            let zombie = Zombie(id: index, name: "Zombie \(index)")
            self.zombieRepository.insert(zombie)
        }
    }
}

// Tests
class ZombieServiceTests<RepositoryType: RepositoryProtocol,
                         ServiceType: ZombieServiceProtocol
                                where ServiceType.RepositoryType == RepositoryType> {
    private var zombieRepository: RepositoryType
    private var zombieService: ServiceType

    init(repository: RepositoryType, service: ServiceType) {
        zombieRepository = repository
        zombieService = service
    }
    func testExample() {
        self.zombieService.fetchZombies()
    }
}
let repositoryMock = RepositoryMock<Zombie>()
let repositoryService = ZombieServiceMock(zombieRepository: repositoryMock)
let zombieTest = ZombieServiceTests(repository: repositoryMock, service: repositoryService)
zombieTest.testExample()

// Prints:
// it's safe out there, all zombies have been deleted
// look, there's another one!
// look, there's another one!
// look, there's another one!
// look, there's another one!
// look, there's another one!

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