i have an issue in swift where i want to check for protocol conformance in a class func and then use some static property when the check succeeds. Here's the playground code:
import UIKit
#objc protocol SearchableObject {
static var sortDescriptors: [NSSortDescriptor] { get }
}
class Test: NSObject {
}
extension Test {
class func loadData() {
if self is SearchableObject {
println(valueForKey("sortDescriptors"))
}
else {
println("not searchable")
}
}
}
class SearchableTest: Test, SearchableObject {
class var sortDescriptors: [NSSortDescriptor] {
return [NSSortDescriptor(key: "property", ascending: true)]
}
}
Test.loadData() // prints "not searchable"
SearchableTest.loadData() // prints "Optional((\n "(property, ascending, compare:)"\n))"
the problem is i can check for protocol conformance, but i can't cast self, that's why i'm using valueForKey().
(self as SearchableObject).sortDescriptors
^ 'SearchableObject' does not have a member named 'sortDescriptors'
casts self to an instance conforming to SearchableObject making the static var inaccessible. As don't like the valueForKey() approach i want to ask whether there is a better way to achieve this?
Thanks in advance :)
In class methods, self is a class, not instance. So the right - but non working - way is:
class func loadData() {
if let cls = self as? SearchableObject.Type {
// ^^^^^
println(cls.sortDescriptors)
// ^ [!] error: accessing members of protocol type value 'SearchableObject.Type' is unimplemented
}
As you can see, it's not implemented :(
No worries, there is a workaround. As long as the protocol is declared as #objc, AnyClass has that properties. You can cast self to AnyClass, then call .sortDescriptors:
class func loadData() {
if self is SearchableObject.Type {
println((self as AnyClass).sortDescriptors)
}
Essentially, this workaround is the same as valueForKey, but it doesn't use strings at least.
self as SearchableObject returns a SearchableObject instance. But you want the class. That's SearchableObject.Type.
So you meant this:
extension Test {
class func loadData() {
if let s = self as? SearchableObject.Type { // <<===
println(s.sortDescriptors)
}
else {
println("not searchable")
}
}
}
But "accessing members of protocol type value...is unimplemented." So the compiler knows about this, and specifically can't handle it currently. Of course all of this is fine if you use instances:
import Foundation
protocol SearchableObject {
var sortDescriptors: [NSSortDescriptor] { get }
}
class Test {}
extension Test {
func loadData() {
if let s = self as? SearchableObject {
println(s.sortDescriptors)
}
else {
println("not searchable")
}
}
}
class SearchableTest: Test, SearchableObject {
static var sharedSortDescriptors = [NSSortDescriptor(key: "property", ascending: true)]
var sortDescriptors: [NSSortDescriptor] { return self.dynamicType.sharedSortDescriptors }
}
Test().loadData() // prints "not searchable"
SearchableTest().loadData()
Related
I'm trying to write some UnitTests for the first time. My pattern is MVP and I'm trying to test my Presenter. I've created mock class: class TeamViewMock: TeamViewPresenterProtocol { }. It contains all the methods from my real Presenter. Inside the each method I'm trying to set the new value for the property, so when the method called - property should get a new value.
Only one property gets new value out of 4 and I've no clue why the other ones didn't get it.
You may see it in the following code
import XCTest
#testable import NHL
class TeamViewPresenterTest: XCTestCase {
var presenter: TeamViewPresenter!
var viewMock: TeamViewMock!
func setupPresenter() {
viewMock = TeamViewMock()
presenter = TeamViewPresenter(with: viewMock)
}
func testGetData() {
setupPresenter()
presenter.getData(completion: {_ in })
XCTAssertTrue(viewMock.isStart) // This one works and returns true
XCTAssertTrue(viewMock.isStop) // Return error
XCTAssertTrue(viewMock.isEndRefreshing) // Return error
XCTAssertTrue(viewMock.isReload) // Return error
}
}
class TeamViewMock: TeamViewPresenterProtocol {
var isStart = false
var isStop = false
var isEndRefreshing = false
var isReload = false
func startAnimating() {
self.isStart = true // Testing stops here and doesn't go any further...
}
func stopAnimating() {
self.isStop = true
}
func endRefreshing() {
self.isEndRefreshing = true
}
func reloadView(_ teams: NHLDTO) {
self.isReload = true
}
}
class TeamViewPresenter {
// MARK: - Public Properties
private weak var view: TeamViewPresenterProtocol?
public let dataFetcherService = DataFetcherService()
// MARK: - Initializers
init(with view: TeamViewPresenterProtocol) {
self.view = view
}
// MARK: - Public Methods
public func getData(completion: #escaping (AppError) -> Void) {
view?.startAnimating() // Testing stops here and doesn't go any further, but still returns true for the property isStart and error for the rest
dataFetcherService.fetchTeamData { [weak self] result in
guard let self = self else { return }
switch result {
case .failure(let error):
completion(error)
print(error)
case .success(let teams):
guard let teams = teams else { return }
self.view?.reloadView(teams)
self.view?.stopAnimating()
self.view?.endRefreshing()
}
}
}
}
protocol TeamViewPresenterProtocol: AnyObject {
func startAnimating()
func stopAnimating()
func reloadView(_ teams: NHLDTO)
func endRefreshing()
}
I have the below code which aims an abstraction -without being have to casting Decodables - for DataModels across the app. I wanted use these DataModels to centrelize them. This is how I far I came right now and I am kind of in dead end.
In this configuration, the code tells me that ProfileResponseDelegate cannot conform to ModelDelegate when ProfileResponseDelegate is a protocol, which makes sense.
protocol ModelDelegate: class {
associatedtype DataType: Decodable
func didReceive(data: DataType)
}
class Model<Type, Delegate: ModelDelegate> where Type == Delegate.DataType {
var data: Type?
weak var delegate: Delegate?
func requestData() { return }
}
protocol ProfileResponseDelegate: ModelDelegate where DataType == ProfileResponse {}
//throws Value of protocol type 'ProfileResponseDelegate' cannot conform to 'ModelDelegate'; only struct/enum/class types can conform to protocols
class ProfileResponseModel: Model<ProfileResponse, ProfileResponseDelegate> {
override func requestData() {
guard let data = data else {
// go to api to get data
return
}
delegate?.didReceive(data: data)
}
}
class Controller: UIViewController, ProfileResponseDelegate {
let model = ProfileResponseModel()
override func viewDidLoad() {
super.viewDidLoad()
model.delegate = self
model.requestData()
}
func didReceive(data: ProfileResponse) {
//tell view code to update regarding data
}
}
When I change ProfileResponseDelegate to be a class -without not being a delegate anymore, but anyway- the code does not allow Controller to inherit from both UIViewController and ProfileResponseDelegate reasoning a class cannot inherit from multiple classes. which again makes sense.
class ProfileResponseDelegate: ModelDelegate {
typealias DataType = ProfileResponse
func didReceive(data: ProfileResponse) {
return
}
}
class Controller: UIViewController, ProfileResponseDelegate {
let model = ProfileResponseModel()
override func viewDidLoad() {
super.viewDidLoad()
model.delegate = self
model.requestData()
}
override func didReceive(data: ProfileResponse) {
//tell view code to update regarding data
}
}
With respect to first configuration, I could not make it work. However for the second one, when Controller just inherits from ProfileResponseDelegate it works just fine.
I have to find a way to make this work -preferably the first configuration- and need your advise. Much appreciated in advance.
UPDATE
So I have removed the associatedType from the ModelDelegate and removed ProfileResponseModel. Right now code looks like this.
protocol ModelDelegate: class {
//associatedtype DataType: Decodable
func didReceive<T: Decodable>(data: T)
}
class Model<Type: Decodable> {
var data: Type?
weak var delegate: ModelDelegate?
func requestData() { return }
}
//protocol ProfileResponseDelegate: ModelDelegate where DataType == ProfileResponse {}
class ProfileResponseModel: Model<ProfileResponse> {
override func requestData() {
guard let data = data else {
// go to api to get data
return
}
delegate?.didReceive(data: data)
}
}
class Controller: UIViewController, ModelDelegate {
let model = ProfileResponseModel()
override func viewDidLoad() {
super.viewDidLoad()
model.delegate = self
model.requestData()
}
func didReceive<T>(data: T) where T : Decodable {
//I want this `data` to come as what it is.
if let response = data as? ProfileResponse {
print(type(of: response))
}
}
}
It works likes this, however my ultimate purpose for doing this to not being have to cast the data to ProfileResponse here -and in other places to other Decodable type-.
I am new to Swift, but I have plenty of experience in other languages like Java, Kotlin, Javascript, etc. It's possible that what I want to do is not supported by the language, and I've poured over the Swift Language Guide looking for the answer.
I want to implement the decorator pattern, using generics. I easily did this in Kotlin, and I'm porting the library to Swift.
class Result<T> {
let result: T?
let error: NSError?
init(result: T?, error: NSError?) {
self.result = result
self.error = error
}
}
protocol DoSomething {
associatedtype T
func doSomething() -> Result<T>
}
protocol StoreSomething {
associatedtype T
func storeSomething(thing: Result<T>)
}
/*
* DOES NOT COMPILE
*/
class StoringSomething<T> {
private let delegate: DoSomething
private let store: StoreSomething
init(delegate: DoSomething, store: StoreSomething) {
self.delegate = delegate
self.store = store
}
func doSomething() -> Result<T> {
let result = delegate.doSomething()
store.storeSomething(thing: result)
return result
}
}
I get a Protocol 'DoSomething' can only be used as a generic constraint because it has Self or associated type requirements error from the compiler. I've tried using a typealias and other ideas from SO and the Swift manual.
Thanks to #Sweeper's suggestion on associatedtype erasure you can implement the Decorator pattern with generics like so:
class AnyDoSomething<T>: DoSomething {
func doSomething() -> Result<T> {
fatalError("Must implement")
}
}
class AnyStoreSomething<T>: StoreSomething {
func storeSomething(thing: Result<T>) {
fatalError("Must implement")
}
}
class StoringSomething<T>: DoSomething {
private let delegate: AnyDoSomething<T>
private let store: AnyStoreSomething<T>
init(delegate: AnyDoSomething<T>, store: AnyStoreSomething<T>) {
self.delegate = delegate
self.store = store
}
func doSomething() -> Result<T> {
let result = delegate.doSomething()
store.storeSomething(thing: result)
return result
}
}
class DoSomethingNice<T>: AnyDoSomething<T> {
override func doSomething() -> Result<T> {
}
}
I have multiple protocols that have the same function name. Some protocols have associated types, where I can't figure out how to call the functions as I do in non-generic protocols. I get the error: Protocol 'MyProtocol1' can only be used as a generic contraint because it has Self or associated type requirements
Here's what I'm trying to do:
protocol Serviceable {
associatedtype DataType
func get(handler: ([DataType] -> Void)?)
}
struct PostService: Serviceable {
func get(handler: ([String] -> Void)? = nil) {
print("Do something...")
}
}
protocol MyProtocol1: class {
associatedtype ServiceType: Serviceable
var service: ServiceType { get }
}
extension MyProtocol1 {
func didLoad(delegate: Self) {
print("MyProtocol1.didLoad()")
}
}
protocol MyProtocol2: class {
}
extension MyProtocol2 {
func didLoad(delegate: MyProtocol2) {
print("MyProtocol2.didLoad()")
}
}
class MyViewController: UIViewController, MyProtocol1, MyProtocol2 {
let service = PostService()
override func viewDidLoad() {
super.viewDidLoad()
didLoad(self as MyProtocol1) // Error here: Protocol 'MyProtocol1' can only be used as a generic contraint because it has Self or associated type requirements
didLoad(self as MyProtocol2)
}
}
How can I specifically call the function from a generic protocol extension?
It's simple to achieve by turning the protocol into a generic (see below), or by creating a type eraser for these protocols, but this very strongly suggests that you have a design problem and you should redesign your classes and/or extensions. A collision like this suggests strongly that MyStruct is doing too many things itself because it's being pulled in multiple directions by MyProtocol1 and MyProtocol2. There should likely be two objects here instead. (Composition rather than inheritance.)
class MyStruct: MyProtocol1, MyProtocol2 {
let service = PostService()
func prot1Load<T: MyProtocol1>(t: T) {
t.didLoad()
}
func prot2Load<T: MyProtocol2>(t: T) {
t.didLoad()
}
init() {
prot1Load(self)
prot2Load(self)
}
}
To your particular example in the comments, I would use composition rather than inheritance. You're treating protocols like multiple-inheritance, which is almost never right. Instead compose out of things that conform to a protocol.
protocol LoadProviding {
func load()
}
struct MyLoader1: LoadProviding {
func load() {
print("MyLoader1.didLoad()")
}
}
struct MyLoader2: LoadProviding {
func load() {
print("MyLoader2.didLoad()")
}
}
protocol Loader {
var loaders: [LoadProviding] { get }
}
extension Loader {
func loadAll() {
for loader in loaders {
loader.load()
}
}
}
class MyStruct: Loader {
let service = PostService()
let loaders: [LoadProviding] = [MyLoader1(), MyLoader2()]
init() {
loadAll()
}
}
Of course you don't really have to have LoadProviding be a full struct. It could just be a function if that's all you need:
typealias LoadProviding = () -> Void
func myLoader1() {
print("MyLoader1.didLoad()")
}
func myLoader2() {
print("MyLoader2.didLoad()")
}
protocol Loader {
var loaders: [LoadProviding] { get }
}
extension Loader {
func loadAll() {
for loader in loaders {
loader()
}
}
}
class MyStruct: Loader {
let service = PostService()
let loaders: [LoadProviding] = [myLoader1, myLoader2]
init() {
loadAll()
}
}
If you have time to wade through a video on the subject, you may be interested in the Beyond Crusty: Real World Protocols talk from dotSwift. It's about this and similar problems.
I'm using Swift 2 and using WeakContainer as a way to store a set of weak objects, much like NSHashTable.weakObjectsHashTable()
struct WeakContainer<T: AnyObject> {
weak var value: T?
}
public protocol MyDelegate : AnyObject {
}
Then in my ViewController, I declare
public var delegates = [WeakContainer<MyDelegate>]
But it is error
Using MyDelegate as a concrete type conforming to protocol AnyObject is not supported
I see that the error is that WeakContainer has value member declared as weak, so T is expected to be object. But I also declare MyDelegate as AnyObject, too. How to get around this?
I ran into the same problem when I tried to implement weak containers. As #plivesey points out in a comment above, this seems to be a bug in Swift 2.2 / Xcode 7.3, but it is expected to work.
However, the problem does not occur for some Foundation protocols. For example, this compiles:
let container = WeakContainer<NSCacheDelegate>()
I found out that this works for protocols marked with the #objc attribute. You can use this as a workaround:
Workaround 1
#objc
public protocol MyDelegate : AnyObject { }
let container = WeakContainer<MyDelegate>() // No compiler error
As this can lead to other problems (some types cannot be represented in Objective-C), here is an alternative approach:
Workaround 2
Drop the AnyObject requirement from the container, and cast the value to AnyObject internally.
struct WeakContainer<T> {
private weak var _value:AnyObject?
var value: T? {
get {
return _value as? T
}
set {
_value = newValue as? AnyObject
}
}
}
protocol MyDelegate : AnyObject { }
var container = WeakContainer<MyDelegate>() // No compiler error
Caveat: Setting a value that conforms to T, but is not an AnyObject, fails.
I had the same idea to create weak container with generics.
As result I created wrapper for NSHashTable and did some workaround for your compiler error.
class WeakSet<ObjectType>: SequenceType {
var count: Int {
return weakStorage.count
}
private let weakStorage = NSHashTable.weakObjectsHashTable()
func addObject(object: ObjectType) {
guard object is AnyObject else { fatalError("Object (\(object)) should be subclass of AnyObject") }
weakStorage.addObject(object as? AnyObject)
}
func removeObject(object: ObjectType) {
guard object is AnyObject else { fatalError("Object (\(object)) should be subclass of AnyObject") }
weakStorage.removeObject(object as? AnyObject)
}
func removeAllObjects() {
weakStorage.removeAllObjects()
}
func containsObject(object: ObjectType) -> Bool {
guard object is AnyObject else { fatalError("Object (\(object)) should be subclass of AnyObject") }
return weakStorage.containsObject(object as? AnyObject)
}
func generate() -> AnyGenerator<ObjectType> {
let enumerator = weakStorage.objectEnumerator()
return anyGenerator {
return enumerator.nextObject() as! ObjectType?
}
}
}
Usage:
protocol MyDelegate : AnyObject {
func doWork()
}
class MyClass: AnyObject, MyDelegate {
fun doWork() {
// Do delegated work.
}
}
var delegates = WeakSet<MyDelegate>()
delegates.addObject(MyClass())
for delegate in delegates {
delegate.doWork()
}
It's not the best solution, because WeakSet can be initialized with any type, and if this type doesn't conform to AnyObject protocol then app will crash. But I don't see any better solution right now.
Why are you trying to use generics? I would suggest doing the following:
import Foundation
import UIKit
protocol MyDelegate : AnyObject {
}
class WeakContainer : AnyObject {
weak var value: MyDelegate?
}
class ViewController: UIViewController {
var delegates = [WeakContainer]()
}
There is also NSValue's nonretainedObject
If your Protocol can be marked as #obj then you can use code below
protocol Observerable {
associatedtype P : AnyObject
var delegates: NSHashTable<P> { get }
}
#objc protocol MyProtocol {
func someFunc()
}
class SomeClass : Observerable {
var delegates = NSHashTable<MyProtocol>.weakObjects()
}
Your issue is that WeakContainer requires its generic type T to be a subtype of AnyObject - a protocol declaration is not a subtype of AnyObject. You have four options:
Instead of declaring WeakContainer<MyDelegate> replace it with something that actually implements MyDelegate. The Swift-y approach for this is to use the AnyX pattern: struct AnyMyDelegate : MyDelegate { ... }
Define MyDelegate to be 'class bound' as protocol MyDelegate : class { ... }
Annotate MyDelegate with #obj which, essentially, makes it 'class bound'
Reformulate WeakContainer to not require its generic type to inherit from AnyObject. You'll be hard pressed to make this work because you need a property declared as weak var and there are limitation as to what types are accepted by weak var - which are AnyObject essentially.
Here is my implementation of WeakSet in pure Swift (without NSHashTable).
internal struct WeakBox<T: AnyObject> {
internal private(set) weak var value: T?
private var pointer: UnsafePointer<Void>
internal init(_ value: T) {
self.value = value
self.pointer = unsafeAddressOf(value)
}
}
extension WeakBox: Hashable {
var hashValue: Int {
return self.pointer.hashValue
}
}
extension WeakBox: Equatable {}
func ==<T>(lhs: WeakBox<T>, rhs: WeakBox<T>) -> Bool {
return lhs.pointer == rhs.pointer
}
public struct WeakSet<Element>: SequenceType {
private var boxes = Set<WeakBox<AnyObject>>()
public mutating func insert(member: Element) {
guard let object = member as? AnyObject else {
fatalError("WeakSet's member (\(member)) must conform to AnyObject protocol.")
}
self.boxes.insert(WeakBox(object))
}
public mutating func remove(member: Element) {
guard let object = member as? AnyObject else {
fatalError("WeakSet's member (\(member)) must conform to AnyObject protocol.")
}
self.boxes.remove(WeakBox(object))
}
public mutating func removeAll() {
self.boxes.removeAll()
}
public func contains(member: Element) -> Bool {
guard let object = member as? AnyObject else {
fatalError("WeakSet's member (\(member)) must conform to AnyObject protocol.")
}
return self.boxes.contains(WeakBox(object))
}
public func generate() -> AnyGenerator<Element> {
var generator = self.boxes.generate()
return AnyGenerator {
while(true) {
guard let box = generator.next() else {
return nil
}
guard let element = box.value else {
continue
}
return element as? Element
}
}
}
}