Merge pull request ochococo#14 from minsOne/master

add observer and Decorator pattern section

Author: ochococo

README.markdown

@@ -326,7 +326,73 @@ tuple.z
 ```
 
 ##🚧  Bridge
-##🚧  Decorator
+##🍧 Decorator
+
+```swift
+protocol Coffee {
+    func getCost() -> Double
+    func getIngredients() -> String
+}
+
+class SimpleCoffee: Coffee {
+    func getCost() -> Double {
+        return 1.0
+    }
+    func getIngredients() -> String {
+        return "Coffee"
+    }
+}
+
+class CoffeeDecorator: Coffee {
+    private let decoratedCoffee: Coffee
+    private let ingredientSeparator: String = ", "
+
+    required init(decoratedCoffee: Coffee) {
+        self.decoratedCoffee = decoratedCoffee
+    }
+    func getCost() -> Double {
+        return decoratedCoffee.getCost()
+    }
+    func getIngredients() -> String {
+        return decoratedCoffee.getIngredients()
+    }
+}
+
+class Milk: CoffeeDecorator {
+    required init(decoratedCoffee: Coffee) {
+        super.init(decoratedCoffee: decoratedCoffee)
+    }
+    override func getCost() -> Double {
+        return super.getCost() + 0.5
+    }
+    override func getIngredients() -> String {
+        return super.getIngredients() + ingredientSeparator + "Milk"
+    }
+}
+
+class WhipCoffee: CoffeeDecorator {
+    required init(decoratedCoffee: Coffee) {
+        super.init(decoratedCoffee: decoratedCoffee)
+    }
+    override func getCost() -> Double {
+        return super.getCost() + 0.7
+    }
+    override func getIngredients() -> String {
+        return super.getIngredients() + ingredientSeparator + "Whip"
+    }
+}
+```
+
+**Usage:**
+```swift
+var someCoffee: Coffee = SimpleCoffee()
+println("Cost : \(someCoffee.getCost()); Ingredients: \(someCoffee.getIngredients())")
+someCoffee = Milk(decoratedCoffee: someCoffee)
+println("Cost : \(someCoffee.getCost()); Ingredients: \(someCoffee.getIngredients())")
+someCoffee = WhipCoffee(decoratedCoffee: someCoffee)
+println("Cost : \(someCoffee.getCost()); Ingredients: \(someCoffee.getIngredients())")
+```
+
 ##🚧  Proxy
 
 #Behavioral
@@ -398,7 +464,35 @@ fileManager.move()
 ##🚧  Iterator
 ##🚧  Mediator
 ##🚧  Memento
-##🚧  Observer
+##📩 Observer
+
+```swift
+class StepCounter {
+    var totalSteps: Int = 0 {
+        willSet(newTotalSteps) {
+            println("About to set totalSteps to \(newTotalSteps)")
+        }
+        didSet {
+            if totalSteps > oldValue  {
+                println("Added \(totalSteps - oldValue) steps")
+            }
+        }
+    }
+}
+```
+**Usage:**
+```swift
+let stepCounter = StepCounter()
+stepCounter.totalSteps = 200
+// About to set totalSteps to 200
+// Added 200 steps
+stepCounter.totalSteps = 360
+// About to set totalSteps to 360
+// Added 160 steps
+stepCounter.totalSteps = 896
+// About to set totalSteps to 896
+// Added 536 steps
+```
 ##🐉 State
 
 ```swift