几种常见语言的命名空间(Namespace)特点
几种常见语言的命名空间(Namespace)特性
命名空间提供了一种从逻辑上组织类的方式，防止命名冲突。
几种常见语言
C++
命名空间是可以嵌套的
嵌套的命名空间是指定义在其他命名空间中的命名空间。嵌套的命名空间是一个嵌套的作用域，内层命名空间声明的名字将隐藏外层命名空间声明的同名成员：
<code class="sourceCode cpp"><span class="dt">int</span> x = <span class="dv">20</span>; <span class="kw">namespace</span> outer { <span class="dt">int</span> x = <span class="dv">10</span>; <span class="kw">namespace</span> inner { <span class="dt">int</span> z = x; } } <span class="dt">int</span> main() { std::cout << outer::inner::z; <span class="co">// 输出10 </span> <span class="kw">return</span> <span class="dv">0</span>; } </code>C#
嵌套的命名空间
命名空间声明中声明命名空间，各命名空间用”.”分隔。
例如:
<code>namespace N1.N2{class A {}class B {}}在语义上等效于namespace N1{namespace N2{class A {}class B {}}} </code>Java
<code class="sourceCode java"><span class="kw">package</span> cn.org.web3d.x3dpad</code>
Java中的命名空间意味着你只要拥有一个独立的顶级域名，就可以保证自己项目的绝对唯一性。
Objective-C
在Objective-C应用中的所有类名都必须是全局唯一的。命名一直是Objective-C的硬伤，和那些优雅的语言相比。苹果官方建议两个字母作为前缀的类名是为官方的库和框架准备的，而对于作为第三方开发者，官方建议使用3个或者更多的字母作为前缀去命名我们的类。
PHP
<code class="sourceCode php"><span class="kw">namespace</span> Vendor\Package\<span class="st">...</span>..</code>
它强调第一级Vendor就应该是唯一性标识，意味着你要拥有一个{Vendor}.com 的顶级域名，才可以保证自己项目的绝对唯一性。比如，当我想到这一点时，我立马去注册了一个meanir.com的域名来防身。
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