added example code for state pattern

Author: Sebastian Boldt

Behavioral.playground/Pages/State.xcplaygroundpage/Contents.swift

@@ -0,0 +1,45 @@
+//: [Previous](@previous)
+
+import Foundation
+
+protocol State {
+    var isAuthorized: Bool { get }
+}
+
+final class UserContext {
+    private var userId: String
+    private var state: State = UnauthorizedState()
+    
+    init(userID: String) {
+        self.userId = userId
+    }
+    
+    var isAuthorized: Bool {
+        self.state.isAuthorized
+    }
+    public func changeToAuthorizedState() {
+        self.state = AuthorizedState()
+    }
+    
+    public func changeToUnauthorizedState() {
+        self.state = UnauthorizedState()
+    }
+}
+
+struct AuthorizedState: State {
+    var isAuthorized: Bool {
+        return true
+    }
+}
+
+struct UnauthorizedState: State {
+    var isAuthorized: Bool {
+        return false
+    }
+}
+
+var context = UserContext(userID: UUID().uuidString)
+context.changeToAuthorizedState()
+context.isAuthorized
+
+//: [Next](@next)

Behavioral.playground/contents.xcplayground

@@ -6,8 +6,9 @@
         <page name='Iterator'/>
         <page name='Strategy'/>
         <page name='Mediator'/>
-        <page name='Observer'/>
         <page name='Visitor'/>
         <page name='Memento'/>
+        <page name='Observer'/>
+        <page name='State'/>
     </pages>
 </playground>

GOFSwift.xcworkspace/xcuserdata/sboldt.xcuserdatad/UserInterfaceState.xcuserstate

@@ -1,6 +1,7 @@
 //: [Previous](@previous)
 
 import Foundation
+import CoreGraphics
 
 protocol Soldier {
     func render(from location: CGPoint, to newLocation: CGPoint)