Swift documentation says that classes, structs, and enums can all conform to protocols, and I can get to a point where they all conform. But I can't get the enum to behave quite like the class and struct examples:
protocol ExampleProtocol {
var simpleDescription: String { get set }
mutating func adjust()
}
class SimpleClass: ExampleProtocol {
var simpleDescription: String = "A very simple class."
var anotherProperty: Int = 69105
func adjust() {
simpleDescription += " Now 100% adjusted."
}
}
var a = SimpleClass()
a.adjust()
let aDescription = a.simpleDescription
struct SimpleStructure: ExampleProtocol {
var simpleDescription: String = "A simple structure"
mutating func adjust() {
simpleDescription += " (adjusted)"
}
}
var b = SimpleStructure()
b.adjust()
let bDescription = b.simpleDescription
enum SimpleEnum: ExampleProtocol {
case Base
var simpleDescription: String {
get {
return "A Simple Enum"
}
set {
newValue
}
}
mutating func adjust() {
self.simpleDescription += ", adjusted"
}
}
var c = SimpleEnum.Base
c.adjust()
let cDescription = c.simpleDescription
I haven't figured out how to get the simpleDescription to change as a result of calling adjust(). My example obviously won't do that because the getter has a value hard-coded, but how can I set a value for the simpleDescription while still conforming to the ExampleProtocol?
This is my attempt:
protocol ExampleProtocol {
var simpleDescription: String { get }
mutating func adjust()
}
enum ExampleEnum : ExampleProtocol {
case Base, Adjusted
var simpleDescription: String {
return self.getDescription()
}
func getDescription() -> String {
switch self {
case .Base:
return "A simple description of enum"
case .Adjusted:
return "Adjusted description of enum"
}
}
mutating func adjust() {
self = ExampleEnum.Adjusted
}
}
var c = ExampleEnum.Base
c.adjust()
let cDescription = c.simpleDescription
Here is my take at it.
As this is an enum and not a class, you have to think different(TM): it is your description that has to change when the "state" of your enum changes (as pointed out by #hu-qiang).
enum SimpleEnumeration: ExampleProtocol {
case Basic, Adjusted
var description: String {
switch self {
case .Basic:
return "A simple Enumeration"
case .Adjusted:
return "A simple Enumeration [adjusted]"
}
}
mutating func adjust() {
self = .Adjusted
}
}
var c = SimpleEnumeration.Basic
c.description
c.adjust()
c.description
Hope that helps.
Here's another approach, using only the knowledge gained from the tour until that point*
enum SimpleEnumeration: String, ExampleProtocol {
case Basic = "A simple enumeration", Adjusted = "A simple enumeration (adjusted)"
var simpleDescription: String {
get {
return self.toRaw()
}
}
mutating func adjust() {
self = .Adjusted
}
}
var c = SimpleEnumeration.Basic
c.adjust()
let cDescription = c.simpleDescription
If you want to have adjust() act as a toggle (although there's nothing to suggest this is the case), use:
mutating func adjust() {
switch self {
case .Basic:
self = .Adjusted
default:
self = .Basic
}
}
*(Although it doesn't explicitly mention how to specify a return type and a protocol)
Here's a solution that doesn't change the current enum value, but their instance values instead (just in case it is useful to anyone).
enum ProtoEnumeration : ExampleProtocol {
case One(String)
case Two(String)
var simpleDescription: String {
get {
switch self {
case let .One(desc):
return desc
case let .Two(desc):
return desc
}
}
}
mutating func adjust() {
switch self {
case let .One(desc):
self = .One(desc + ", adjusted 1")
case let .Two(desc):
self = .Two(desc + ", adjusted 2")
}
}
}
var p = ProtoEnumeration.One("test")
p.simpleDescription
p.adjust()
p.simpleDescription
It is not possible to define variables without getter and setter in enums and therefore it is impossible to have a variable that you can modify.
You can conform to the protocol but you cannot have same behavior with mutating as in classes.
It is a link about enum in swift.
Structures and enumerations are value types. By default, the properties of a value type cannot be modified from within its instance methods. link
Then, you have to use mutating function.
enum ProtocolEnum: ExampleProtocol {
case on, off
var simpleDescription: String {
switch self {
case .on:
return "Switch is ON"
case .off:
return "Switch is OFF"
}
}
mutating func adjust() {
switch self {
case .on:
self = off
case .off:
self = on
}
}
}
var c = ProtocolEnum.on
c.simpleDescription
c.adjust()
let cDescription = c.simpleDescription
Another option is for adjust() to flip between cases as follows:
enum SimpleEnum: ExampleProtocol {
case Foo, Bar
var simpleDescription: String {
get {
let value = self == .Foo
? "Foo"
: "Bar"
return "A simple \(value) enum."
}
}
mutating func adjust() {
self = self == .Foo
? .Bar
: .Foo
}
}
Here's building on Jack's answer:
protocol ICanWalk {
var description: String { get }
mutating func stepIt()
}
enum TwoStepsForwardThreeStepsBack: Int, ICanWalk {
case Base = 0, Step1, Step2
var description: String {
return "Step \(self.rawValue)"
}
mutating func stepIt() {
if let nextStep = TwoStepsForwardThreeStepsBack( rawValue: self.rawValue + 1 ) {
// going forward.
self = nextStep
} else {
// back to the base.
self = TwoStepsForwardThreeStepsBack.Base
}
}
}
I came up with this
protocol ExampleProtocol {
var simpleDescription: String { get }
mutating func adjust()
}
enum Seat: ExampleProtocol {
case WindowSeat, MiddleSeat, AisleSeat
var simpleDescription : String {
switch self {
case .WindowSeat:
return "Window Seat"
case .MiddleSeat:
return "Middle Seat"
case .AisleSeat:
return "Aisle Seat"
}
}
mutating func adjust() {
switch self {
case .WindowSeat:
self = .MiddleSeat
case .MiddleSeat:
self = . AisleSeat
case .AisleSeat:
self = .WindowSeat
}
}
}
var seat = Seat.MiddleSeat
print(seat.simpleDescription) // Middle Seat
seat.adjust()
print(seat.simpleDescription) // Aisle Seat
Another variation: Using associated values to hold and display previous option
(of the form "Selected 1, adjusted from 2, adjusted from 1, adjusted from 2, adjusted from 1")
protocol ExampleProtocol {
var simpleDescription: String { get }
mutating func adjust()
}
indirect enum EnumWithDescription: ExampleProtocol {
case option1(EnumWithDescription?)
case option2(EnumWithDescription?)
var simpleDescription: String {
return "Selected " + getDescription()
}
internal func getDescription() -> String {
var currentValue: String
let previousValue : EnumWithDescription?
switch self {
case .option1(let previous):
currentValue = "1"
previousValue = previous
case .option2(let previous):
currentValue = "2"
previousValue = previous
}
if let adjustedFrom = previousValue?.getDescription() {
return "\(currentValue) adjusted from \(adjustedFrom)"
}
else {
return "\(currentValue)"
}
}
mutating func adjust() {
switch self {
case .option1:
self = .option2(self)
case .option2:
self = .option1(self)
}
}
}
var d = EnumWithDescription.option1(nil)
d.simpleDescription
d.adjust()
d.adjust()
d.simpleDescription
// Output: "Selected 1, adjusted from 2, adjusted from 1, adjusted from 2, adjusted from 1"
here's my code
enum SimpleEnum: ExampleProtocol {
case Base, Adjusted
var simpleDescription: String {
get {
var description = "A simple enum."
switch self {
case .Base:
return description
case .Adjusted:
return description + " - [adjusted]"
}
}
}
mutating func adjust() {
self = SimpleEnum.Adjusted
}
}
var simpleEnum = SimpleEnum.Base
simpleEnum.adjust()
simpleEnum.simpleDescription
My first contribution here:
enum SimpleEnum: ExampleProtocol {
case Basic(String), Adjusted(String)
init() {
self = SimpleEnum.Basic("A simple Enum")
}
var simpleDescription: String {
get {
switch self {
case let .Basic(string):
return string
case let .Adjusted(string):
return string
}
}
}
mutating func adjust() {
self = SimpleEnum.Adjusted("full adjusted")
}
}
var c = SimpleEnum()
c.adjust()
let cDescription = c.simpleDescription
Thanks for others!
This experiment threw me off too, due to the previous SimpleClass and SimpleStructure examples showing the property simpleDescription being modified internally, which caused me to think that I needed to do the same thing. After looking over the other answers posted here and reading the official Apple Swift 2.1 documentation, I came up with this:
protocol ExampleProtocol {
var simpleDescription: String { get }
mutating func adjust()
}
enum SimpleEnum: ExampleProtocol {
case Simple
case Adjusted
var simpleDescription: String {
switch self {
case .Simple:
return "A simple enumeration"
case .Adjusted:
return "A simple enumeration somewhat changed."
}
}
mutating func adjust() {
self = .Adjusted
}
mutating func restore() {
self = .Simple
}
}
var d: SimpleEnum = .Simple
d.simpleDescription
d.adjust()
d.simpleDescription
d.restore()
d.simpleDescription
Also notice that in the examples given by Apple for SimpleClass and SimpleStructure prior to this experiment, the simple description is lost internally - you cannot get the original value back (unless of course you save it outside of the class/structure); this is what prompted me to create a restore() method for the SimpleEnum example, which allows you to toggle it back and forth between values. Hope this is useful to someone!
I was thinking that the goal is simply to retain state and use a description to make the current state easier to read:
enum SimpleEnum: ExampleProtocol {
case Default, Adjusted
init() {
self = .Default
}
var simpleDescription: String { get { return "\(self) Value" }}
mutating func adjust() {
self = .Adjusted
}
}
var simpleEnum = SimpleEnum()
simpleEnum.adjust()
let adjustedSimple = simpleEnum.simpleDescript
how about this
enum SimpleEnum : ExampleProtocol {
case Desc(String)
init() {
self = Desc("a simple enum")
}
var simpleDescription:String {
get {
return (Mirror(reflecting: self).children.first!.value as? String)!
}
}
mutating func adjust() {
self = SimpleEnum.Desc(self.desc + " adjusted")
}
}
var e = SimpleEnum()
e.simpleDescription # => "a simple enum"
e.adjust()
e.simpleDescription # => "a simple enum adjusted"
Related
I was trying to make an extension for safe unwrapping, and I was working in 2 version of it, one long code form, second short code! But unexpectedly they do not work! So far as I can see to my code, I just made all things correct! What I am missing to fix both version?
struct ContentView: View {
let test: String? = "Hello, World!"
var body: some View {
Text(test.safeUnwrapV1(defaultValue: "Empty!"))
Text(test.safeUnwrapV2(defaultValue: "Empty!"))
}
}
extension Optional {
func safeUnwrapV1<T>(defaultValue: T) -> T {
let wrappedValue: T? = (self as? T?) ?? nil
if let unwrappedValue: T = wrappedValue { return unwrappedValue }
else { return defaultValue }
}
func safeUnwrapV2<T>(defaultValue: T) -> T {
return (self as? T) ?? defaultValue
}
}
There's no need to define your own generic type parameter. Optional is already generic and its generic type parameter is called Wrapped. So you simply need to declare the type of the default value to be Wrapped.
extension Optional {
func defaultValue(_ value: Wrapped) -> Wrapped {
self ?? value
}
}
struct ContentView: View {
let test: String? = "Hello, World!"
var body: some View {
Text(test.defaultValue("Empty!"))
}
}
extension Optional {
func safeUnwrap(_ defaultValue: Wrapped) -> Wrapped {
switch self {
case let value?: return value
case nil: return defaultValue
}
}
}
Or even
extension Optional {
func safeUnwrap(_ defaultValue: Wrapped) -> Wrapped {
self ?? defaultValue
}
}
But as was pointed out, this is more wordy and less idiomatic than just using the ?? operator.
Make your extension like this.
extension Optional {
func safeUnwrapV1<T>(defaultValue: T) -> Wrapped {
guard let value = self else {
return defaultValue as! Wrapped
}
return value
}
}
EDIT: As #Rudedog suggest no need to define generic here
extension Optional {
func safeUnwrapV1(defaultValue: Wrapped) -> Wrapped {
guard let value = self else {
return defaultValue
}
return value
}
}
I would constrain Optional generic Wrapped type to LosslessStringConvertible:
extension LosslessStringConvertible {
var string: String { .init(self) }
}
extension Optional where Wrapped: LosslessStringConvertible {
var string: String { self?.string ?? "" }
func string(default value: Wrapped) -> String {
self?.string ?? value.string
}
}
Usage:
var double1 = Double("2.7")
var double2 = Double("a")
print(double1.string(default: 0))
print(double2.string(default: 0))
This would print:
2.7
0
From within a property wrapper in Swift, can you someone refer back to the instance of the class or struck that owns the property being wrapped? Using self doesn't obviously work, nor does super.
I tried to pass in self to the property wrapper's init() but that doesn't work either because self on Configuration is not yet defined when #propertywrapper is evaluated.
My use case is in a class for managing a large number of settings or configurations. If any property is changed, I just want to notify interested parties that something changed. They don't really need to know which value just, so use something like KVO or a Publisher for each property isn't really necessary.
A property wrapper looks ideal, but I can't figure out how to pass in some sort of reference to the owning instance that the wrapper can call back to.
References:
SE-0258
enum PropertyIdentifier {
case backgroundColor
case textColor
}
#propertyWrapper
struct Recorded<T> {
let identifier:PropertyIdentifier
var _value: T
init(_ identifier:PropertyIdentifier, defaultValue: T) {
self.identifier = identifier
self._value = defaultValue
}
var value: T {
get { _value }
set {
_value = newValue
// How to callback to Configuration.propertyWasSet()?
//
// [self/super/...].propertyWasSet(identifier)
}
}
}
struct Configuration {
#Recorded(.backgroundColor, defaultValue:NSColor.white)
var backgroundColor:NSColor
#Recorded(.textColor, defaultValue:NSColor.black)
var textColor:NSColor
func propertyWasSet(_ identifier:PropertyIdentifier) {
// Do something...
}
}
The answer is no, it's not possible with the current specification.
I wanted to do something similar. The best I could come up with was to use reflection in a function at the end of init(...). At least this way you can annotate your types and only add a single function call in init().
fileprivate protocol BindableObjectPropertySettable {
var didSet: () -> Void { get set }
}
#propertyDelegate
class BindableObjectProperty<T>: BindableObjectPropertySettable {
var value: T {
didSet {
self.didSet()
}
}
var didSet: () -> Void = { }
init(initialValue: T) {
self.value = initialValue
}
}
extension BindableObject {
// Call this at the end of init() after calling super
func bindProperties(_ didSet: #escaping () -> Void) {
let mirror = Mirror(reflecting: self)
for child in mirror.children {
if var child = child.value as? BindableObjectPropertySettable {
child.didSet = didSet
}
}
}
}
You cannot do this out of the box currently.
However, the proposal you refer to discusses this as a future direction in the latest version:
https://github.com/apple/swift-evolution/blob/master/proposals/0258-property-wrappers.md#referencing-the-enclosing-self-in-a-wrapper-type
For now, you would be able to use a projectedValue to assign self to.
You could then use that to trigger some action after setting the wrappedValue.
As an example:
import Foundation
#propertyWrapper
class Wrapper {
let name : String
var value = 0
weak var owner : Owner?
init(_ name: String) {
self.name = name
}
var wrappedValue : Int {
get { value }
set {
value = 0
owner?.wrapperDidSet(name: name)
}
}
var projectedValue : Wrapper {
self
}
}
class Owner {
#Wrapper("a") var a : Int
#Wrapper("b") var b : Int
init() {
$a.owner = self
$b.owner = self
}
func wrapperDidSet(name: String) {
print("WrapperDidSet(\(name))")
}
}
var owner = Owner()
owner.a = 4 // Prints: WrapperDidSet(a)
My experiments based on : https://github.com/apple/swift-evolution/blob/master/proposals/0258-property-wrappers.md#referencing-the-enclosing-self-in-a-wrapper-type
protocol Observer: AnyObject {
func observableValueDidChange<T>(newValue: T)
}
#propertyWrapper
public struct Observable<T: Equatable> {
public var stored: T
weak var observer: Observer?
init(wrappedValue: T, observer: Observer?) {
self.stored = wrappedValue
}
public var wrappedValue: T {
get { return stored }
set {
if newValue != stored {
observer?.observableValueDidChange(newValue: newValue)
}
stored = newValue
}
}
}
class testClass: Observer {
#Observable(observer: nil) var some: Int = 2
func observableValueDidChange<T>(newValue: T) {
print("lol")
}
init(){
_some.observer = self
}
}
let a = testClass()
a.some = 4
a.some = 6
The answer is yes! See this answer
Example code for calling ObservableObject publisher with a UserDefaults wrapper:
import Combine
import Foundation
class LocalSettings: ObservableObject {
static var shared = LocalSettings()
#Setting(key: "TabSelection")
var tabSelection: Int = 0
}
#propertyWrapper
struct Setting<T> {
private let key: String
private let defaultValue: T
init(wrappedValue value: T, key: String) {
self.key = key
self.defaultValue = value
}
var wrappedValue: T {
get {
UserDefaults.standard.object(forKey: key) as? T ?? defaultValue
}
set {
UserDefaults.standard.set(newValue, forKey: key)
}
}
public static subscript<EnclosingSelf: ObservableObject>(
_enclosingInstance object: EnclosingSelf,
wrapped wrappedKeyPath: ReferenceWritableKeyPath<EnclosingSelf, T>,
storage storageKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Setting<T>>
) -> T {
get {
return object[keyPath: storageKeyPath].wrappedValue
}
set {
(object.objectWillChange as? ObservableObjectPublisher)?.send()
UserDefaults.standard.set(newValue, forKey: object[keyPath: storageKeyPath].key)
}
}
}
I am trying to create a couple of objects which are dependent one to each other and they mush have a method to downcast directly the concrete class of the other object. Something like this:
protocol aProt
{
var bVar:bProt! { get set }
}
protocol bProt
{
var aVar:aProt! { get set }
}
class a: aProt
{
var bVar: bProt!
func bConcrete() -> b {
return bVar as! b
}
}
class b: bProt
{
var aVar: aProt!
func aConcrete() -> a {
return aVar as! a
}
Now, the problem is that I want this behavior (func aConcrete(),func bConcrete()) to be inherited by the subclasses of a and b. Then I thought the perfect way of doing this was using generics, but... There's no way of doing this.
class a: aProt
{
var bVar: bProt!
func bConcrete() -> T {
return bVar as! T
}
}
class b: bProt
{
var aVar: aProt!
func aConcrete<T>() -> T {
return aVar as! T
}
You can do it but when you have to use it you must downcast the variable anyway, so there is no way of doing it in a clean manner:
let aObject = a()
let bSubclassObject = a.bConcrete() // The compiler complains it cannot infer the class of T
let bSubclassObject = a.bConcrete() as! bSubclass // this works, but this is exactly which I wanted to avoid... :(
Define the generic function and add where to T:
protocol aProt {
var bVar: bProt! { get set }
}
protocol bProt {
var aVar:aProt! { get set }
}
class a: aProt {
var bVar: bProt!
func bConcrete<T: b>(_ type: T.Type) -> T? {
return bVar as? T
}
}
class b: bProt {
var aVar: aProt!
func aConcrete<T: a>(_ type: T.Type) -> T? {
return aVar as? T
}
}
class a1: a { }
class b1: b {
var fullName: String = "new object"
}
let aObj = a()
aObj.bVar = b1()
let bObj = aObj.bConcrete(b1.self)
bObj?.fullName
According to your requirement, calls bConcrete(b1.self) might still not good enough, but at least you need to know what type of data you are expecting to return.
I have a simple enum that I would like to iterate over. For this purpose, I've adopted Sequence and IteratorProtocol as shown in the code below. BTW, this can be copy/pasted to a Playground in Xcode 8.
import UIKit
enum Sections: Int {
case Section0 = 0
case Section1
case Section2
}
extension Sections : Sequence {
func makeIterator() -> SectionsGenerator {
return SectionsGenerator()
}
struct SectionsGenerator: IteratorProtocol {
var currentSection = 0
mutating func next() -> Sections? {
guard let item = Sections(rawValue:currentSection) else {
return nil
}
currentSection += 1
return item
}
}
}
for section in Sections {
print(section)
}
But the for-in loop generates the error message "Type 'Sections.Type' does not conform to protocol 'Sequence'".
The protocol conformance is in my extension; so, what is wrong with this code?
I know there are other ways of doing this but I'd like to understand what's wrong with this approach.
Thanks.
Note that Martin’s solution can be refactored as a protocol:
import Foundation
protocol EnumSequence
{
associatedtype T: RawRepresentable where T.RawValue == Int
static func all() -> AnySequence<T>
}
extension EnumSequence
{
static func all() -> AnySequence<T> {
return AnySequence { return EnumGenerator() }
}
}
private struct EnumGenerator<T: RawRepresentable>: IteratorProtocol where T.RawValue == Int {
var index = 0
mutating func next() -> T? {
guard let item = T(rawValue: index) else {
return nil
}
index += 1
return item
}
}
Then, given an enum
enum Fruits: Int {
case apple, orange, pear
}
you slap the protocol and a typealias:
enum Fruits: Int, EnumSequence {
typealias T = Fruits
case apple, orange, pear
}
Fruits.all().forEach({ print($0) }) // apple orange pear
Update: As of Swift 4.2, you can simply add protocol conformance
to CaseIterable, see How to enumerate an enum with String type?.
You can iterate over a value of a type which conforms to the Sequence
protocol. Therefore
for section in Sections.Section0 {
print(section)
}
would compile and give the expected result. But of course that is not
really what you want because the choice of the value is arbitrary and the
value itself not needed in the sequence.
As far as I know, there is no way to iterate over a type itself, so that
for section in Sections {
print(section)
}
compiles. That would require that the "metatype" Sections.Type conforms
to Sequence. Perhaps someone proves me wrong.
What you can do is to define a type method which returns a sequence:
extension Sections {
static func all() -> AnySequence<Sections> {
return AnySequence {
return SectionsGenerator()
}
}
struct SectionsGenerator: IteratorProtocol {
var currentSection = 0
mutating func next() -> Sections? {
guard let item = Sections(rawValue:currentSection) else {
return nil
}
currentSection += 1
return item
}
}
}
for section in Sections.all() {
print(section)
}
Simply add to enum:
static var allTypes: [Sections] = [.Section0, .Section1, .Section2]
And than you can:
Sections.allTypes.forEach { (section) in
print("\(section)")
}
This looks so much simpler:
public protocol EnumSequence {
init?(rawValue: Int)
}
public extension EnumSequence {
public static var items: [Self] {
var caseIndex: Int = 0
let interator: AnyIterator<Self> = AnyIterator {
let result = Self(rawValue: caseIndex)
caseIndex += 1
return result
}
return Array(interator)
}
}
Iterated upon the solutions above, see below a protocol that can be implemented by enumerations to add the allValues sequence but also to allow the possibility to convert to and from string value.
Very convenient for String-like enumerations which need to support objective c (only int enumerations are allowed there).
public protocol ObjcEnumeration: LosslessStringConvertible, RawRepresentable where RawValue == Int {
static var allValues: AnySequence<Self> { get }
}
public extension ObjcEnumeration {
public static var allValues: AnySequence<Self> {
return AnySequence {
return IntegerEnumIterator()
}
}
public init?(_ description: String) {
guard let enumValue = Self.allValues.first(where: { $0.description == description }) else {
return nil
}
self.init(rawValue: enumValue.rawValue)
}
public var description: String {
return String(describing: self)
}
}
fileprivate struct IntegerEnumIterator<T: RawRepresentable>: IteratorProtocol where T.RawValue == Int {
private var index = 0
mutating func next() -> T? {
defer {
index += 1
}
return T(rawValue: index)
}
}
For a concrete example:
#objc
enum Fruit: Int, ObjcEnumeration {
case apple, orange, pear
}
Now you can do:
for fruit in Fruit.allValues {
//Prints: "apple", "orange", "pear"
print("Fruit: \(fruit.description)")
if let otherFruit = Fruit(fruit.description), fruit == otherFruit {
print("Fruit could be constructed successfully from its description!")
}
}
If your enum is an Int based one, you can do an effective but slightly dirty trick like this.
enum MyEnum: Int {
case One
case Two
}
extension MyEnum {
func static allCases() -> [MyEnum] {
var allCases = [MyEnum]()
for i in 0..<10000 {
if let type = MyEnum(rawValue: i) {
allCases.append(type)
} else {
break
}
}
return allCases
}
}
Then loop over MyEnum.allCases()..
I would like to use enum with associated values for type-safe NSNotifications:
enum Notification {
case Foo(Int)
case Bar
var rawValue: String {
switch self {
case .Foo:
return "Foo"
case .Bar:
return "Bar"
}
}
var asNSNotification: NSNotification {
let userInfo = [String: AnyObject]()
switch self {
case let .Foo(intVal):
userInfo["intVal": intVal]
default:
break
}
return NSNotification(name: rawValue, object: nil, userInfo: userInfo)
}
init?(fromNSNotification n: NSNotification) {
switch n.name {
case .Bar:
self = .Bar
case .Foo(42): // some bogus value
let realValue = n.userInfo?["intVal"] ?? 0
self = .Foo(realValue)
default:
return nil
}
}
}
This should work, but it sure is an ugly piece of code. Anyone has ideas how to make it more elegant?
EDIT: the reason why I want to use enum is to make parameters of each notification type-safe.
By "more elegant" I mean:
Simplify rawValue property (avoid having to switch)
Avoid "bogus values" when referencing enum cases with associated values in
initializer.
Anything that would reduce verbosity and improve
readability.
Okay, here's how rawValue property can be simplified:
var rawValue: String {
return Mirror(reflecting: self).children.first.flatMap({ $0.label }) ?? "\(self)"
}
It seems to me that your enum is working too hard. This should be sufficient:
enum Notification {
case Foo(Int)
case Bar
func notification() -> NSNotification {
switch self {
case Foo(let intVal):
return NSNotification(name: "Foo", object: nil, userInfo: ["IntVal":intVal])
case Bar:
return NSNotification(name: "Bar", object: nil)
}
}
}
Adding the ability to supply a non-nil object is left as an exercise for the reader.
I think I have figured out how to make the handling of NSNotifications more elegant:
enum NotificationType: String {
case Foo
case Bar
}
enum Notification {
case Foo(Int)
case Bar
// the fragile part
var type: NotificationType {
let name = Mirror(reflecting: self).children.first.flatMap({ $0.label }) ?? "\(self)"
return NotificationType(rawValue: name)!
}
var asNSNotification: NSNotification {
let name = type.rawValue
let userInfo = [String: AnyObject]()
switch self {
case let .Foo(intVal):
userInfo["intVal": intVal]
default:
break
}
return NSNotification(name: name, object: nil, userInfo: userInfo)
}
init?(fromNSNotification n: NSNotification) {
let type = NotificationType(rawValue: n.name)!
switch type {
case .Bar:
self = .Bar
case .Foo:
let value = n.userInfo?["intVal"] ?? 0
self = .Foo(value)
default:
return nil
}
}
}
This solution relies on the convention that case names in Notification and NotificationType are the same. One might say that such design is fragile, but I think this is little tradeoff compared to what we achieve.
Below is a little helper class to handle subscription/unsubscription:
protocol NotificationReceiving: class {
func didReceiveNotification(notification: Notification)
}
class NotificationReceiver {
private weak var delegate: NotificationReceiving?
private(set) var subscriptions = Set<NotificationType>()
init(delegate: NotificationReceiving?) {
self.delegate = delegate
}
func subscribe(notificationTypes: NotificationType...) {
let nc = NSNotificationCenter.defaultCenter()
let doSubscribe: NotificationType -> Void = {
nc.addObserver(self, selector: "handleNotification:", name: $0.name, object: nil)
self.subscriptions.insert($0)
}
notificationTypes.forEach(doSubscribe)
}
func unsubscribe(notificationTypes: NotificationType...) {
let nc = NSNotificationCenter.defaultCenter()
if notificationTypes.isEmpty {
nc.removeObserver(self)
} else {
let doUnsubscribe: NotificationType -> Void = {
nc.removeObserver(self, name: $0.name, object: nil)
self.subscriptions.remove($0)
}
notificationTypes.forEach(doUnsubscribe)
}
}
#objc private func handleNotification(notification: NSNotification) {
if let n = Notification(fromNSNotification: notification) {
delegate?.didReceiveNotification(n)
}
}
}
This is how a client might look:
class Client: NotificationReceiving {
private var receiver: NotificationReceiver!
init() {
receiver = NotificationReceiver(delegate: self)
receiver.subscribe(.Foo, .Bar)
}
deinit {
receiver.unsubscribe()
}
func didReceiveNotification(notification: Notification) {
switch notification {
case let .Foo(val):
print("foo with val: \(val)")
// this notification is one-shot:
receiver.unsubscribe(.Foo)
case .Bar:
print("bar!")
}
}
}
Not sure handling all notifications in one method is good design (I guess it might get messy when there are many notifications), but the point is that we can now use the power of type safety and pattern matching, which is awesome.