From f48f70eb83b2acd46515661f0f20c94a9e5706e8 Mon Sep 17 00:00:00 2001
From: jaywcjlove <398188662@qq.com>
Date: Thu, 29 Dec 2016 01:55:07 +0800
Subject: [PATCH] =?UTF-8?q?=E7=90=86=E8=A7=A3=E5=8F=AF=E9=80=89=E7=B1=BB?=
 =?UTF-8?q?=E5=9E=8B?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 README.md             | 26 ++++++++++++++++++++++++++
 examples/demo20.swift | 17 +++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 examples/demo20.swift

diff --git a/README.md b/README.md
index 128ddf3..fd9f638 100644
--- a/README.md
+++ b/README.md
@@ -528,6 +528,29 @@ let arrays: Array<Int> = [1, 1, 1, 1]
 - 类型后面用问号 `?` 表示可选类型；
 - 类型后面用感叹号 `!` 表示隐式可选类型；
 
+### 可选类型
+
+当基础类型（整形、浮点、布尔等）没有值时，是不能使用的。Swift 为了表达这种状态，对类型提供了可选的概念。在某个类型后面添加 ? 可以表示一个可选类型，这个可选类型有两种状态：1. 有值；2. 没值
+
+```swift
+var optionalInteger: Int?
+optionalInteger = 404
+
+if optionalInteger != nil {   // 确定可选类型包含值后可以在变量名后加!强制解析
+    print(optionalInteger!)   // 404
+}
+
+var errorCode: Int? = 404  // 在类型后面添加一个?
+print(errorCode)           // Optional(404)  // 会打印警告
+errorCode = nil            // 对非可选类型赋值为nil会报错
+print(errorCode)           // nil            // 会打印警告
+
+// 确定可选类型包含值后可以在变量名后加!强制解析
+if errorCode != nil {
+    print(errorCode!)// 404
+}
+```
+
 ## 问题解决
 
 - [swift NameError: name 'run_one_line' is not defined](https://github.com/Homebrew/homebrew-core/issues/2712)
@@ -536,6 +559,9 @@ let arrays: Array<Int> = [1, 1, 1, 1]
 ## 参考教程
 
 - [The Swift Programming Language 中文版](http://special.csdncms.csdn.net/the-swift-programming-language-in-chinese/Introduction.shtml)
+- [官方文档The Swift Programming Language](https://swift.org/documentation/#the-swift-programming-language)
+- [官方文档的中文版The Swift Programming Language中文版](https://github.com/numbbbbb/the-swift-programming-language-in-chinese)
+- [Swift3.0语法速查手册](https://darielchen.github.io/SwiftManual/)
 - [深入浅出 Swift 3](https://www.shiyanlou.com/courses/611)
 - [Swift教程](http://c.biancheng.net/cpp/swift/jiaocheng/)
 - [慕课网Swift教程](http://www.imooc.com/search/course?words=swift)
diff --git a/examples/demo20.swift b/examples/demo20.swift
new file mode 100644
index 0000000..d9b82ef
--- /dev/null
+++ b/examples/demo20.swift
@@ -0,0 +1,17 @@
+var optionalInteger: Int?
+optionalInteger = 404
+
+if optionalInteger != nil {                  // 确定可选类型包含值后可以在变量名后加!强制解析
+    print(optionalInteger!)                  // 404
+}
+
+
+var errorCode: Int? = 404  // 在类型后面添加一个?
+print(errorCode)        // Optional(404)
+errorCode = nil         // 对非可选类型赋值为nil会报错
+print(errorCode)        // nil
+
+// 确定可选类型包含值后可以在变量名后加!强制解析
+if errorCode != nil {
+    print(errorCode!)// 404
+}
\ No newline at end of file