🌸 Add chapter 7 starter playground

Chapter 07 - Getting Started with Combine/starter/Getting Started with Combine Playground.playground/Pages/Introduction.xcplaygroundpage/Contents.swift

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+/*:
+ # Getting Started with Combine
+
+ * Created by [Peter Friese](https://twitter.com/peterfriese) – [peterfriese.dev](https://peterfriese.dev)
+
+ This playground is designed to show how Combine works. It accompanies chapter 8 in "Asynchronous Programming with SwiftUI and Combine"
+
+ ## Overview
+ * [Simple Publishers](Simple%20Publishers)
+ * [Pizza Ordering, Part 1](Pizza%20Ordering,%20Part%201)
+ * [Pizza Ordering, Part 2](Pizza%20Ordering,%20Part%202)
+ * [Pizza Ordering, Part 3](Pizza%20Ordering,%20Part%203)
+ * [Manually Assembling Publishers and Subscribers](Manually%20Assembling%20Publishers%20and%20Subscribers)
+ * [Publishers](Publishers)
+
+ [Next >](@next)
+ */

Chapter 07 - Getting Started with Combine/starter/Getting Started with Combine Playground.playground/Pages/Manually Assembling Publishers and Subscribers.xcplaygroundpage/Contents.swift

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+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)
+
+import Foundation
+import Combine
+import UIKit
+
+enum OrderStatus: String {
+  case placed
+  case processing
+  case delivered
+}
+
+extension Notification.Name {
+  static let didUpdateOrderStatus = Notification.Name(rawValue: "didUpdateOrderStatus")
+}
+
+class Order {
+  var status: OrderStatus
+  var item: String
+
+  init(item: String) {
+    self.status = .placed
+    self.item = item
+  }
+}
+
+let sushi = Order(item: "Bento box #1")
+let orderPublisher = NotificationCenter.Publisher(center: .default, name: .didUpdateOrderStatus, object: sushi)
+
+let orderSubscriber = Subscribers.Sink<Notification, Never> { completion in
+  //  print(completion)
+  print("Received completion")
+} receiveValue: { value in
+  //  print(value.name)
+  //  if let status = value.userInfo?["status"] as? OrderStatus {
+  //    print(status.rawValue)
+  //  }
+  print("Received value: \(value)")
+}
+orderPublisher.subscribe(orderSubscriber)
+
+NotificationCenter.default.publisher(for: .didUpdateOrderStatus, object: sushi)
+  .sink { notifiaction in
+    print("Received notification: \(notifiaction)")
+  }
+
+
+let info = [
+  "newStatus": OrderStatus.processing,
+]
+NotificationCenter.default.post(name: .didUpdateOrderStatus, object: sushi, userInfo: info)
+
+
+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)

Chapter 07 - Getting Started with Combine/starter/Getting Started with Combine Playground.playground/Pages/Pizza Ordering, Part 1.xcplaygroundpage/Contents.swift

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+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)
+// Publishers
+
+import Foundation
+import Combine
+
+// create the order
+
+
+// the following code won't compile, so we need to use an operator to convert the `Notification` to an `OrderStatus`
+//pizzaOrderPublisher
+//  .assign(to: \.status, on: pizzaOrder)
+
+
+
+// once the user is ready to place the order
+
+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)

Chapter 07 - Getting Started with Combine/starter/Getting Started with Combine Playground.playground/Pages/Pizza Ordering, Part 2.xcplaygroundpage/Contents.swift

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+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)
+// Composing Operators
+
+import Foundation
+import Combine
+
+
+
+
+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)

Chapter 07 - Getting Started with Combine/starter/Getting Started with Combine Playground.playground/Pages/Pizza Ordering, Part 3.xcplaygroundpage/Contents.swift

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+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)
+// Combining Publishers
+
+import Foundation
+import Combine
+
+let margheritaOrder = Order(toppings: [
+    Topping("tomatoes", isVegan: true),
+    Topping("vegan mozzarella", isVegan: true),
+    Topping("basil", isVegan: true)
+])
+
+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)

Chapter 07 - Getting Started with Combine/starter/Getting Started with Combine Playground.playground/Pages/Publishers.xcplaygroundpage/Contents.swift

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+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)
+
+import Foundation
+import Combine
+
+let answerPublisher = Just(42)
+
+let answerSubscriber = Subscribers.Sink<Int, Never> { completion in
+  print("Received completion")
+} receiveValue: { value in
+  print("I received value \(value) from publisher")
+}
+
+answerPublisher.subscribe(answerSubscriber)
+
+
+let answerSubscription = answerPublisher.sink { value in
+  print("Received value \(value) from publisher")
+}
+
+
+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)

Chapter 07 - Getting Started with Combine/starter/Getting Started with Combine Playground.playground/Pages/Simple Publishers.xcplaygroundpage/Contents.swift

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+/*: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)
+
+ # Publishers and Subscribers
+
+ **Publishers** and **subscribers** are a key concept of Combine.
+
+ - A `Publisher` emits values over time, and delivers them to one or more subscribers
+ - A `Subscriber` receives a stream of elements from a publisher
+ */
+
+import Foundation
+import Combine
+
+/*:
+ `Just` publishes _just_ one value and then completes.
+ */
+Just(42)
+
+/*:
+ **Note** that a publisher will only start publishing once there is a subscription.
+ Here we're adding `sink`, which is a generic subscriber, and then print the received value.
+ */
+Just(42)
+  .print()
+  .sink { value in
+    print("Received \(value)")
+  }
+
+print("---")
+
+/*:
+ A collectiom can be turned into a publisher by invoking `.publisher` on it.
+ */
+["Pepperoni", "Mushrooms", "Onions", "Sausage", "Bacon", "Extra cheese", "Black olives", "Green peppers"].publisher
+  .sink { topping in
+    print("\(topping) is a favourite topping for pizza")
+  }
+
+/*:
+ `String` is a collection, so using `.publisher` will emit all the characters in the string as individual values, which might not be what you were expecting.
+ */
+"Combine".publisher
+  .sink { value in
+    print("Hello \(value)")
+  }
+
+/*:
+ If you want to publish a single string, use `Just` instead.
+ */
+Just("Combine")
+  .sink { value in
+    print("Hello \(value)")
+  }
+
+//: [<Previous](@previous)  [Home](Introduction)  [Next>](@next)

Chapter 07 - Getting Started with Combine/starter/Getting Started with Combine Playground.playground/Sources/PizzaOrderHelpers.swift

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+import Foundation
+
+public struct Topping {
+  public var name: String
+  public var isVegan: Bool
+
+  public init(_ name: String, isVegan: Bool) {
+    self.name = name
+    self.isVegan = isVegan
+  }
+}
+
+public enum OrderStatus: String {
+  case placing
+  case placed
+  case processing
+  case delivered
+}
+
+public enum AddressStatus: String {
+  case invalid
+  case valid
+}
+
+public extension Notification.Name {
+  static let addTopping = Notification.Name(rawValue: "addTopping")
+  static let didUpdateOrderStatus = Notification.Name(rawValue: "didUpdateOrderStatus")
+
+  static let didValidateAddress = Notification.Name(rawValue: "didValidateAddress")
+}
+
+public class Order {
+  public var status: OrderStatus {
+    willSet {
+      print("Status of order is now [\(newValue)]")
+    }
+  }
+  public var toppings: [Topping]?
+  public var addressStatus: AddressStatus
+
+  public init() {
+    self.status = .placing
+    self.addressStatus = .invalid
+  }
+
+  public convenience init(toppings: [Topping]) {
+    self.init()
+    self.toppings = toppings
+  }
+}
+

Chapter 07 - Getting Started with Combine/starter/Getting Started with Combine Playground.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8"?>
+<playground version="6.0" target-platform="ios" requires-full-environment="false">
+    <pages>
+        <page name="Introduction"/>
+        <page name="Simple Publishers"/>
+        <page name="Pizza Ordering, Part 1"/>
+        <page name="Pizza Ordering, Part 2"/>
+        <page name="Pizza Ordering, Part 3"/>
+        <page name="Manually Assembling Publishers and Subscribers"/>
+        <page name="Publishers"/>
+    </pages>
+</playground>