IOS中的四种变量修饰关键字 @private @protected @public @package

文档上记录是这样的

The Scope of Instance Variables

To enforce the ability of an object to hide its data, the compiler limits the scope of instance variables—that is, limits their visibility within the program.

为了强制一个对象隐藏其数据，编译器限制实例变量范围以限制其在程序中的可见性

But to provide flexibility, it also lets you explicitly set the scope at four levels. Each level is marked by a compiler directive:

可是为了提供灵活性，苹果也让开发者显式设置范围（四选一）

Directive	Meaning
@private	The instance variable is accessible only within the class that declares it.
@protected	实例变量只能被声明它的类访问 The instance variable is accessible within the class that declares it and within classes that inherit it. All instance variables without an explicit scope directive have@protectedscope. 实例变量能被声明它的类和子类访问，全部没有显式制定范围的实例变量都是@protected
@public	The instance variable is accessible everywhere. 实例变量能够被在任何地方访问。
@package	Using the modern runtime, an@packageinstance variable has@publicscope inside the executable p_w_picpath that implements the class, but acts like@privateoutside.使用modern运行时，一个@package实例变量在实现这个类的可执行文件镜像中其实是@public的，可是在外面就是@private【runtime须要再看一下苹果文档Runtime Programming Guide】 The@packagescope for Objective-C instance variables is analogous toprivate_externfor C variables and functions. Any code outside the class implementation’s p_w_picpath that tries to use the instance variable gets a link error. Objective-C中的@package与C语言中变量和函数的private_extern相似。任何在实现类的镜像以外的代码想使用这个实例变量都会引起link error This scope is most useful for instance variables in framework classes, where@privatemay be too restrictive but@protectedor@publictoo permissive. 这个类型最经常使用于框架类的实例变量，使用@private太限制，使用@protected或者@public又太开放