Finished doc for keypaths

Author: Bob Lee

course/swift4/generic-subscripts.md

@@ -1,10 +1,14 @@
 # Generic Subscripts
+Welcome to one of the least favored lessons of all time. Hopefully, this lesson is nice and short since I don't like using subscripts at all. Let's get started.
 
 ## Introduction
+
 ## Problem
 Can subscripts return `T`?
 
 ### Your past
+You remember in Chapter 1, this is probably how I introduced you to subscripts in Swift, whose role is to provide a shortcut.
+
 ```swift
 struct WeekDays {
   private var days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
@@ -16,19 +20,29 @@ struct WeekDays {
 }
 ```
 
+Well, we can make it a little bit more complex and potentially more scalable.
+
+### JSON
+A `json` file looks like below.
+
+```json
+{
+  "name": "Bob",
+  "age": 21,
+  "favoriteFood": ["Pizza", "Carbonara", "Hamburger"]
+}
+```
+
 ### Introducing Generic Subscripts
+Let us create how to "design" a `json` like structure in Swift by using `Dictionary`.
+
 ```swift
 struct JSON {
   private var storage: [String: Any]
 
   init(dictionary: [String: Any]) {
     self.storage = dictionary
   }
-
-  subscript<T>(key: String) -> T? {
-    return storage[key] as? T
-  }
-}
 ```
 
 ### Create JSON
@@ -40,16 +54,40 @@ let republicOfKorea = JSON(dictionary: [
   ])
 ```
 
+### Introducing Generic Subscripts
+```swift
+struct JSON {
+  private var storage: [String: Any]
+
+  init(dictionary: [String: Any]) {
+    self.storage = dictionary
+  }
+
+  subscript<T>(key: String) -> T? {
+    return storage[key] as? T
+  }
+}
+```
+
+
 ### Access Value
+Let us use the generic subscript method above.
 ```swift
-let koreaCaital: String? = republicOfKorea["capital"]
+let koreaCapital: String? = republicOfKorea["capital"]
 let koreaName: String? = republicOfKorea["name"]
 let koreaPopulation: Int? = republicOfKorea["population"]
 ```
 
+Make sure you define `T?` from `any` explicitly as shown as `koreaCapital: String?`.
 
+### My Opinion
+I don't recommend using Subscripts even if it provides generics because there isn't much context available and it takes much effort to search through.
 
 ### Source Code
+[9003_generic_subscripts]()
+
 ### Resources
+[Generic Subscripts - Apple](https://github.com/apple/swift-evolution/blob/master/proposals/0148-generic-subscripts.md)
 
 ## Conclusion
+Just to recap, in the very first chapter, you've learned that Swift provides a shortcut for accessing methods and properties. However, I warned you because that shortcut comes along with a big tradeoff. First, it is hard to found and second, it does not provide context unless the name of an object does. Also, even if you use generic subscripts, I don't like the fact that I have to explicitly define the placeholder type of `T`. It definitely can cause a huge issue for your teammates if they have not read or understand the object he/she is working with. So, I recommend not to use them. But, of course, if it is something quick and easy. feel free to.

course/swift4/keypaths.md

@@ -73,6 +73,6 @@ rob[keyPath: nameKeyPath] // "Rob"
 [Smart KeyPaths: Better Key-Value Coding for Swift - Apple](https://github.com/apple/swift-evolution/blob/master/proposals/0161-key-paths.md)
 
 ## Conclusion
-Congratulations. Remember, even if you are chaining through, you may make a single mistake that leads to catastrophic result. Although it is a brand new feature, if you need to access Property or Method through many chainings, I recommend you to utilize the keypath feature provided in Swift 4.
+Congratulations. Remember, even if you are chaining through, you may make a single auto-completion mistake that leads to catastrophic result. Although it is a brand new feature, if you need to access Property or Method through many chainings, I recommend you to utilize the keypath API provided in Swift 4. If you want to learn much deeper, feel free to take a look at the Apple's proposal documentation in the lecture notes.
 
-In the following lesson, you will learn how to make subscripts generic. 
+In the following lesson, you will learn how to make subscripts generic, which isn't that important but at least you can brag from what you've learned.

source-code/9000_swift4/.DS_Store

@@ -1,7 +1,7 @@
 /*:
  ## Learn Swift with Bob
  ### What's New in Swift 4
- ### Generic Subscripts
+ ### 9003_Generic Subscripts
 
  **Problem:** Can subscripts return `T`?
 

source-code/9000_swift4/9003_generic_subscripts.playground/Pages/8001_nested_generics_recursive_enum.xcplaygroundpage/Contents.swift renamed to source-code/9000_swift4/9003_generic_subscripts.playground/Pages/9003_generic_subscripts.xcplaygroundpage/Contents.swift

@@ -1,2 +1,2 @@
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
-<playground version='6.0' target-platform='ios' display-mode='raw'/>
+<playground version='6.0' target-platform='ios' display-mode='rendered'/>