Here's the protocol oriented code i have for which i am stuck with for writing unit tests.
protocol TestProtocol {
func testOne()
func testTwo()
}
extension TestProtocol {
var testHelper: TestHelper {
return TestHelper()
}
fileprivate func _one() {
testHelper.one()
}
func one() {
_one()
}
fileprivate func _two() {
testHelper.two()
}
func two() {
_two()
}
}
struct TestHelper {
var userDefaults: UserDefaults {
return UserDefaults.standard
}
func one() {
userDefaults.set("12223334444", forKey: "PhoneNumberWithCountryCode")
}
func two() {
userDefaults.set("Mark", forKey: "UserName")
}
}
class TestAboveCode { }
extension TestAboveCode: TestProtocol {
func testOne() {
_one()
}
func testTwo() {
_two()
}
}
class UseAboveCode {
func use() {
TestAboveCode().testOne()
}
}
here's the problem,
To write unit test for UseAboveCode class, i need to mock the TestHelper struct. Though i can create a mock struct and override the existing functions, i cannot set the testHelper property in the TestProtocol extension. Is there a work around for this?
I do know the other approach which is making the TestHelper struct implement a protocol and ultimately injecting that as a property or through a constructor. This code above looks ideal for readability and usability but someone i am not able to wrap my head around unit test.
Am i over thinking with this approach? Please let me know what the best approach is.
Related
I have the following class:
class MyClass<T: BaseClass> {
let aThing = T()
func someMethod() {
configure()
}
}
whereas
class SubTypeAOfBaseClass: BaseClass { ... }
class SubTypeBOfBaseClass: BaseClass { ... }
In configure I want to configure aThing depending on its type. Therefore I have created a protocol Configurable and an extension:
protocol Configurable {
func configure()
}
extension MyClass: Configurable where T == SubTypeAOfBaseClass {
func configure() {
print("Configuring SubTypeAOfBaseClass")
aThing.doSomethingA()
}
}
The error that I get is in MyClass.someMethod where I call configure(): "Referencing instance method configure() requires types T and SubTypeAOfBaseClass be equivalent.
Another error when I add the following extension:
extension MyClass: Configurable where T == SubTypeBOfBaseClass {
func configure() {
print("Configuring SubTypeBOfBaseClass")
aThing.doSomethingB()
}
}
The error changes to "No exact matches in call to instance method configure" and in the line
extension MyClass: Configurable where T == SubTypeBOfBaseClass {
I get the error "Conflicting conformance of MyClass to protocol configurable, there cannot more than one conformance, even with different conditional bounds."
It should work, but apparently I am missing something or my understanding of how to achieve what I want is wrong.
Consider the case when T is BaseClass, or when T is AnotherSubclass that I defined as
class AnotherSubclass : BaseClass {
}
What would happen? You haven't declared a conformance to Configure when T is AnotherSubclass!
There's really only two (not bad) choices here.
You want configure to do nothing when T is neither SubTypeAOfBaseClass nor SubTypeBOfBaseClass
you only want MyClass<SubTypeAOfBaseClass> and MyClass<SubTypeBOfBaseClass> to be valid types - MyClass<BaseClass> and MyClass<AnotherSubclass> would give compiler errors.
Choice 2 is not possible in Swift. That would require something similar to the sealed types in Java or Kotlin.
Choice 1 can be done like this:
class BaseClass {
...
func configure() {
}
}
class SubTypeAOfBaseClass: BaseClass {
...
override func configure() {
print("Configuring SubTypeAOfBaseClass")
doSomethingA()
}
}
class SubTypeBOfBaseClass: BaseClass {
...
override func configure() {
print("Configuring SubTypeAOfBaseClass")
doSomethingB()
}
}
class MyClass<T: BaseClass> {
let aThing = T()
func someMethod() {
aThing.configure()
}
}
You might notice that the each implementation of configure has been moved to the base classes. If you want to implement them all in MyClass, you must check the type by hand:
class MyClass<T: BaseClass> {
let aThing = T()
func someMethod() {
if let selfA = self as? MyClass<SubTypeAOfBaseClass> {
selfA.configure()
} else if let selfB = self as? MyClass<SubTypeBOfBaseClass> {
selfB.configure()
}
}
}
extension MyClass where T == SubTypeAOfBaseClass {
func configure() {
print("Configuring SubTypeAOfBaseClass")
aThing.doSomethingA()
}
}
extension MyClass where T == SubTypeBOfBaseClass {
func configure() {
print("Configuring SubTypeBOfBaseClass")
aThing.doSomethingB()
}
}
This is because of the second problem in your code - different parameterisations of a generic type, MyClass<SubTypeAOfBaseClass> and MyClass<SubTypeBOfBaseClass>, can't conform to a protocol differently. This is a limitation of Swift, unfortunately. See here for more info.
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.
Is it possible to add the same methods to different classes?
Example:
class FilterableTable: UITableViewController { ... }
class FilterableCollection: UICollectionViewController { ... }
extension FilterableTable, FilterableCollection { // I know this line is wrong
func filterItems(){ print('filtered!') }
}
How can I add the same Foo method to a UICollectionViewController?
Protocols allow to declare only needed methods signatures, but I need exactly the same method (with body), to avoid copy-paste...
You can use the Protocol Extensions to do what you need. Extensions are new and allow for a default implementation of the protocol methods. I modified your code just a bit so it would compile.
class FilterableTable: FilterType {
init() {}
}
class FilterableCollection: FilterType {
init() {}
}
protocol FilterType {
func filterItems()
}
extension FilterType { // I know this line is wrong
func filterItems(){ print("filtered!") }
}
let a = FilterableTable()
a.filterItems()
let b = FilterableCollection()
b.filterItems()
Check out the section on Protocol Extensions. Swift Programming Guide
Actual answer: Use the Delegates, Luke!
class FilterableTable: UITableViewController {
var filterDelegate: FilterDelegate!
func viewDidLoad(){
filterDelegate = Filter()
}
}
class FilterableCollection: UICollectionViewController {
var filterDelegate: FilterDelegate!
func viewDidLoad(){
filterDelegate = Filter()
}
}
protocol FilterDelegate {
func filterItems()
}
class Filter: FilterDelegate {
func filterItems() {
print("Hooray!")
}
}
Is there a way to create an abstract class in the Swift Language, or is this a limitation just like Objective-C? I'd like to create a abstract class comparable to what Java defines as an abstract class.
There are no abstract classes in Swift (just like Objective-C). Your best bet is going to be to use a Protocol, which is like a Java Interface.
With Swift 2.0, you can then add method implementations and calculated property implementations using protocol extensions. Your only restrictions are that you can't provide member variables or constants and there is no dynamic dispatch.
An example of this technique would be:
protocol Employee {
var annualSalary: Int {get}
}
extension Employee {
var biweeklySalary: Int {
return self.annualSalary / 26
}
func logSalary() {
print("$\(self.annualSalary) per year or $\(self.biweeklySalary) biweekly")
}
}
struct SoftwareEngineer: Employee {
var annualSalary: Int
func logSalary() {
print("overridden")
}
}
let sarah = SoftwareEngineer(annualSalary: 100000)
sarah.logSalary() // prints: overridden
(sarah as Employee).logSalary() // prints: $100000 per year or $3846 biweekly
Notice that this is providing "abstract class" like features even for structs, but classes can also implement the same protocol.
Also notice that every class or struct that implements the Employee protocol will have to declare the annualSalary property again.
Most importantly, notice that there is no dynamic dispatch. When logSalary is called on the instance that is stored as a SoftwareEngineer it calls the overridden version of the method. When logSalary is called on the instance after it has been cast to an Employee, it calls the original implementation (it doesn't not dynamically dispatch to the overridden version even though the instance is actually a Software Engineer.
For more information, check great WWDC video about that feature: Building Better Apps with Value Types in Swift
Note that this answer is targeted at Swift 2.0 and above
You can achieve the same behaviour with protocols and protocol extensions.
First, you write a protocol that acts as an interface for all the methods that have to be implemented in all types that conform to it.
protocol Drivable {
var speed: Float { get set }
}
Then you can add default behaviour to all types that conform to it
extension Drivable {
func accelerate(by: Float) {
speed += by
}
}
You can now create new types by implementing Drivable.
struct Car: Drivable {
var speed: Float = 0.0
init() {}
}
let c = Car()
c.accelerate(10)
So basically you get:
Compile time checks that guarantee that all Drivables implement speed
You can implement default-behaviour for all types that conform to Drivable (accelerate)
Drivable is guaranteed not to be instantiated since it's just a protocol
This model actually behaves much more like traits, meaning you can conform to multiple protocols and take on default implementations of any of them, whereas with an abstract superclass you're limited to a simple class hierarchy.
I think this is the closest to Java's abstract or C#'s abstract:
class AbstractClass {
private init() {
}
}
Note that, in order for the private modifiers to work, you must define this class in a separate Swift file.
EDIT: Still, this code doesn't allow to declare an abstract method and thus force its implementation.
The simplest way is to use a call to fatalError("Not Implemented") into the abstract method (not variable) on the protocol extension.
protocol MyInterface {
func myMethod() -> String
}
extension MyInterface {
func myMethod() -> String {
fatalError("Not Implemented")
}
}
class MyConcreteClass: MyInterface {
func myMethod() -> String {
return "The output"
}
}
MyConcreteClass().myMethod()
After I struggled for several weeks, I finally realized how to translate a Java/PHP abstract class to Swift:
public class AbstractClass: NSObject {
internal override init(){}
public func getFoodToEat()->String
{
if(self._iAmHungry())
{
return self._myFavoriteFood();
}else{
return "";
}
}
private func _myFavoriteFood()->String
{
return "Sandwich";
}
internal func _iAmHungry()->Bool
{
fatalError(__FUNCTION__ + "Must be overridden");
return false;
}
}
public class ConcreteClass: AbstractClass, IConcreteClass {
private var _hungry: Bool = false;
public override init() {
super.init();
}
public func starve()->Void
{
self._hungry = true;
}
public override func _iAmHungry()->Bool
{
return self._hungry;
}
}
public protocol IConcreteClass
{
func _iAmHungry()->Bool;
}
class ConcreteClassTest: XCTestCase {
func testExample() {
var concreteClass: ConcreteClass = ConcreteClass();
XCTAssertEqual("", concreteClass.getFoodToEat());
concreteClass.starve();
XCTAssertEqual("Sandwich", concreteClass.getFoodToEat());
}
}
However I think Apple did not implement abstract classes because it generally uses the delegate+protocol pattern instead. For example the same pattern above would be better done like this:
import UIKit
public class GoldenSpoonChild
{
private var delegate: IStomach!;
internal init(){}
internal func setup(delegate: IStomach)
{
self.delegate = delegate;
}
public func getFoodToEat()->String
{
if(self.delegate.iAmHungry())
{
return self._myFavoriteFood();
}else{
return "";
}
}
private func _myFavoriteFood()->String
{
return "Sandwich";
}
}
public class Mother: GoldenSpoonChild, IStomach
{
private var _hungry: Bool = false;
public override init()
{
super.init();
super.setup(self);
}
public func makeFamilyHungry()->Void
{
self._hungry = true;
}
public func iAmHungry()->Bool
{
return self._hungry;
}
}
protocol IStomach
{
func iAmHungry()->Bool;
}
class DelegateTest: XCTestCase {
func testGetFood() {
var concreteClass: Mother = Mother();
XCTAssertEqual("", concreteClass.getFoodToEat());
concreteClass.makeFamilyHungry();
XCTAssertEqual("Sandwich", concreteClass.getFoodToEat());
}
}
I needed this kind of pattern because I wanted to commonize some methods in UITableViewController such as viewWillAppear etc. Was this helpful?
There is a way for simulating abstract classes using Protocols.
This is an example:
protocol MyProtocol {
func doIt()
}
class BaseClass {
weak var myDelegate: MyProtocol?
init() {
...
}
func myFunc() {
...
self.myDelegate?.doIt()
...
}
}
class ChildClass: BaseClass, MyProtocol {
override init(){
super.init()
self.myDelegate = self
}
func doIt() {
// Custom implementation
}
}
One more way how you can implement abstract class is to block initializer.
I've done it this way:
class Element:CALayer { // IT'S ABSTRACT CLASS
override init(){
super.init()
if self.dynamicType === Element.self {
fatalError("Element is abstract class, do not try to create instance of this class")
}
}
}
It's a really old question but still… Here's a snippet of actual code that compiles on Swift 5.2 and works as intended:
protocol Context {
init() throws
func out(_ aStr: String) throws
// Other stuff
}
class AbstractContext: Context {
required init() throws {
if Self.self === AbstractContext.self {
preconditionFailure("Call to abstract method \(Self.self).\(#function)")
}
}
func out(_ aStr: String) throws {
preconditionFailure("Call to abstract method \(Self.self).\(#function)")
}
// Other stuff
}
class CompileContext: AbstractContext {
required init() throws {}
override func out(_ aStr: String) throws {
print(aStr)
}
// Other stuff
}
And here's what I get once I remove CompileContext.out:
Fatal error: Call to abstract method CompileContext.out(_:): file swiftpg/contexts.swift, line 28
With the limitation of no dynamic dispatch, you could do something like this:
import Foundation
protocol foo {
static var instance: foo? { get }
func prt()
}
extension foo {
func prt() {
if Thread.callStackSymbols.count > 30 {
print("super")
} else {
Self.instance?.prt()
}
}
}
class foo1 : foo {
static var instance : foo? = nil
init() {
foo1.instance = self
}
func prt() {
print("foo1")
}
}
class foo2 : foo {
static var instance : foo? = nil
init() {
foo2.instance = self
}
func prt() {
print("foo2")
}
}
class foo3 : foo {
static var instance : foo? = nil
init() {
foo3.instance = self
}
}
var f1 : foo = foo1()
f1.prt()
var f2 : foo = foo2()
f2.prt()
var f3 : foo = foo3()
f3.prt()
I was trying to make a Weather abstract class, but using protocols wasn't ideal since I had to write the same init methods over and over again. Extending the protocol and writing an init method had it's issues, especially since I was using NSObject conforming to NSCoding.
So I came up with this for the NSCoding conformance:
required init?(coder aDecoder: NSCoder) {
guard type(of: self) != Weather.self else {
fatalError("<Weather> This is an abstract class. Use a subclass of `Weather`.")
}
// Initialize...
}
As for init:
fileprivate init(param: Any...) {
// Initialize
}
Move all references to abstract properties and methods of Base class to protocol extension implementation, where Self constraint to Base class. You will gain access to all methods and properties of Base class. Additionally compiler check implementation of abstract methods and properties in protocol for derived classes
protocol Commom:class{
var tableView:UITableView {get};
func update();
}
class Base{
var total:Int = 0;
}
extension Common where Self:Base{
func update(){
total += 1;
tableView.reloadData();
}
}
class Derived:Base,Common{
var tableView:UITableView{
return owner.tableView;
}
}
I want to implement an observer pattern, but I do not find the proper programming language constructs in Swift (also 2.0). The main problems are:
protocol and extension does not allow stored properties.
In classes we could add stored properties, but we can not force a subclass to override some of its inherited methods.
This is what I want:
{class|protocol|extension|whathaveyou} Sensor {
var observers = Array<Any>() // This is not possible in protocol and extensions
// The following is does not work in classes
func switchOn()
func switchOff()
var isRunning : Bool {
get
}
}
class LightSensor : Sensor {
//...
override func switchOn() {
// turn the sensor on
}
}
// In the class C, implementing the protocol 'ObserverProtocol'
var lightSensor = LightSensor()
lightSensor.switchOn()
lightSensor.registerObserver(self) // This is what I want
And here comes what is possible to my knowledge:
class Sensor {
private var observers = Array<Observer>()
func registerObserver(observer:ObserverDelegate) {
observers.append(observer)
}
}
protocol SensorProtocol {
func switchOn()
func switchOff()
var isRunning : Bool {
get
}
}
class LightSensor : Sensor, SensorProtocol {
func switchOn() {
//
}
func switchOff() {
//
}
var isRunning : Bool {
get {
return // whatever
}
}
}
But this is not very convenient, because both Sensor and SensorProtocol should come hand in hand, and are both requirements the subclass LightSensor has to fulfill.
Any ideas?
A protocol is an abstract set of requirements shared across a number of (potentially very different) other objects. As such, it's illogical to store data in a protocol. That would be like global state. I can see that you want to define the specification for how the observers are stored though. That would also allow 'you' to remove 'someone else' from being an observer, and it's very restrictive about how the observers are stored.
So, your protocol should expose methods to add and remove 'yourself' as an observer. It's then the responsibility of the object implementing the protocol to decide how and where the observers are stored and to implement the addition and removal.
You could create a struct to work with your protocols, something like:
protocol Observer: class {
func notify(target: Any)
}
protocol Observable {
mutating func addObserver(observer: Observer)
mutating func removeObserver(observer: Observer)
}
struct Observation: Observable {
var observers = [Observer]()
mutating func addObserver(observer: Observer) {
print("adding")
observers.append(observer)
}
mutating func removeObserver(observer: Observer) {
print("removing")
for i in observers.indices {
if observers[i] === observer {
observers.removeAtIndex(i)
break
}
}
}
func notify(target: Any) {
print("notifying")
for observer in observers {
observer.notify(target)
}
}
}
struct ATarget: Observable {
var observation = Observation()
mutating func addObserver(observer: Observer) {
observation.addObserver(observer)
}
mutating func removeObserver(observer: Observer) {
observation.removeObserver(observer)
}
func notifyObservers() {
observation.notify(self)
}
}
class AnObserver: Observer {
func notify(target: Any) {
print("notified!")
}
}
let myObserver = AnObserver()
var myTarget: Observable = ATarget()
myTarget.addObserver(myObserver)
if let myTarget = myTarget as? ATarget {
myTarget.notifyObservers()
}
This is my solution in Swift 3
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
var objectToObserve = ObjectToObserve()
let observer = Observer()
let observer1 = Observer()
objectToObserve.add(observer: observer, notifyOnRegister: true)
objectToObserve.add(observer: observer1, notifyOnRegister: true)
}
}
//
// MARK: Protocol
//
protocol Observing: class {
func doSomething()
func doSomethingClosure(completion: () -> Void)
}
protocol Observable {
}
extension Observable {
private var observers: [Observing] {
get {
return [Observing]()
}
set {
//Do nothing
}
}
mutating func add(observer: Observing, notifyOnRegister: Bool) {
if !observers.contains(where: { $0 === observer }) {
observers.append(observer)
if notifyOnRegister {
observer.doSomething()
observer.doSomethingClosure(completion: {
print("Completion")
})
}
}
}
mutating func remove(observer: Observing) {
observers = observers.filter({ $0 !== observer })
}
}
//
// MARK: Observing
//
class ObjectToObserve: Observable {
init() {
print("Init ObjectToObserve")
}
}
class Observer: Observing {
init() {
print("Init Observer")
}
func doSomething() {
print("Do something")
}
func doSomethingClosure(completion: () -> Void) {
print("Do something Closure")
completion()
}
}
All answers above incorrectly use an array for retaining the observers, which may create retain cycles because of the strong references.
Also in general you may not want to allow the same observer to register itself twice.
The presented solutions also are not general purpose or lack type safety. I reference my blog post here which presents a full solution in a Swifty manner:
https://www.behindmedia.com/2017/12/23/implementing-the-observer-pattern-in-swift/
Well, you can certainly overcome the restriction of not having stored properties on extensions.
Maybe that way you can complement one of the proposed solutions with an extension that helps you avoid creating the observer list in each subclass / protocol implementation.
Although extensions can't have stored properties, you can actually get them by using the Objective-C Runtime. Assuming you have a base class for your sensors (BaseSensor) and a protocol for observers (SensorObserver):
import Foundation
import ObjectiveC
private var MyObserverListKey: UInt8 = 0
extension BaseSensor {
var observers:[SensorObserver] {
get {
if let observers = objc_getAssociatedObject( self, &MyObserverListKey ) as? [SensorObserver] {
return observers
}
else {
var observers = [SensorObserver]()
objc_setAssociatedObject( self, &MyObserverListKey, observers, objc_AssociationPolicy(OBJC_ASSOCIATION_RETAIN_NONATOMIC) )
return observers
}
}
set(value) {
objc_setAssociatedObject( self, &MyObserverListKey, observers, objc_AssociationPolicy(OBJC_ASSOCIATION_RETAIN_NONATOMIC) )
}
}
}
To be clear, even though you would need BaseSensor and all Sensors to inherit from it in order to have this property, BaseSensor wouldn't actually implement the Sensor protocol.
It's a bit weird, but I think it would suit your needs:
class BaseSensor {
}
protocol Sensor {
func switchOn()
}
class LightSensor: BaseSensor, Sensor {
func switchOn() {
// whatever
}
}
With Swift 2.0 this would be much simpler, since you can use Protocol Extensions, so you could simply do this:
protocol Sensor {
func switchOn()
}
extension Sensor {
// Here the code from the previous implementation of the extension of BaseSensor
}
class LightSensor : Sensor {
func switchOn() {
// whatever
}
}
Way better.