Namespace characteristics of several common languages

Namespace provides a way to organize classes logically and prevent naming conflicts.

Several common languages ​​

C++

Namespaces can be nested

Nested namespaces refer to namespaces defined in other namespaces. A nested namespace is a nested scope. The name declared in the inner namespace will hide the members of the same name declared in the outer namespace:

<code><span>int</span> x = <span>20</span>; 
<span>namespace</span> outer { 
  <span>int</span> x = <span>10</span>; 
  <span>namespace</span> inner { 
    <span>int</span> z = x; 
  } 
} 
  
<span>int</span> main() 
{ 
  std::cout << outer::inner::z; <span>// 输出10 </span><span>return</span><span>0</span>; 
} </code>

C#

Nested namespace

In the namespace declaration Declare the namespace and separate each namespace with ".".

For example:

<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><span>package</span> cn.org.web3d.x3dpad</code>

The namespace in Java means that as long as you have an independent top-level domain name, you can ensure the absolute uniqueness of your project.

Objective-C

All class names in Objective-C applications must be globally unique. Naming has always been a weakness of Objective-C, compared with those elegant languages. Apple officially recommends that class names with two letters as prefixes are prepared for official libraries and frameworks. For third-party developers, the official recommendation is to use 3 or more letters as prefixes to name our classes.

PHP

<code><span>namespace</span> Vendor\Package\<span>...</span>..</code>

It emphasizes that the first-level Vendor should be a unique identifier, which means that you must have a top-level domain name of {Vendor}.com to ensure the absolute uniqueness of your project. For example, when I thought about this, I immediately registered a domain name of meanir.com to protect myself.

The above has introduced the namespace features of several common languages, including aspects of the content. I hope it will be helpful to friends who are interested in PHP tutorials.