finish Variables section

Variables.playground/Contents.swift

@@ -1,13 +1,56 @@
 import Foundation
 
-
+// let变量不可变
 let myName = "Gary"
 let yourName = "Foo"
 
-
+// var变量可以改变
+// structur
 var names = [
     myName,
     yourName
 ]
 
-names.append("fjflajfa")
+names.append("Mike")
+
+// 值拷贝
+let foo = "Foo"
+var foo2 = foo
+foo2 = "Foo2"
+foo
+
+let moreName = [
+    "Gary",
+    "Mike",
+    "Sara"
+]
+
+// let -> var
+var copy = moreName
+copy.append("Foo")
+moreName
+
+// class 指针传递，let只保证指针不改变
+let oldArray = NSMutableArray(
+    array: ["Mike", "Paul"]
+)
+
+oldArray.add("Baz")
+
+var newArray = oldArray
+newArray.add("Qux")
+newArray
+oldArray
+
+
+// 一些函数签名表示不改变变量，实际上改变
+let someNames = NSMutableArray(
+    array: ["Mike", "Paul"]
+)
+func changTheArray(_ array: NSArray) {
+    let copy_address = array as! NSMutableArray
+    copy_address.add("Bazz")
+}
+
+changTheArray(someNames)
+someNames