IOS: Learning notes, Swift namespaces

In Swift, namespaces are implemented using Class (extension) nesting, which is shown in a simple example.

////Main.swift//Swiftnamespace////Created by Yao_yu on 14-8-1.//Copyright (c) 2014 Yao_yu. All rights reserved.////Swift namespace usage examples//Import Foundation//defining the top-level namespacesclassyy{}//define second-level namespaces in YY namespaces testextension yy{classtest{}}//defining a point class in a two-tier namespaceextension YY. test{classpoint2d{var x:double=0var y:double=0Init (_ x:double, _ y:double) {self.x=x self.y=y}}}func Main () {//Point of Usevar pt = YY. TEST.POINT2D (123,333) println ("point coordinates are (\ (pt.x), \ (PT.Y))")        //The result is a point coordinate of (123.0,333.0)}main ()