Usage of php namespace

php namespace usage: [namespace Article;] means creating a namespace named Article. It should be noted that there cannot be any code in front of the first namespace of the current script file.

One of the clearest purposes of namespaces is to solve the problem of duplicate names. In PHP, two functions or classes are not allowed to have the same name, otherwise a fatal error will occur. mistake. In this case, it can be solved as long as you avoid naming duplication. The most common way is to agree on a prefix.

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Namespace divides the code into different spaces (regions), and the constants, functions, and classes of each space (for To be lazy, I will call them elements below) whose names do not affect each other. This is somewhat similar to the concept of 'encapsulation' that we often mention.

To create a namespace, you need to use the namespace keyword, like this:

<?php
//创建一个名为&#39;Article&#39;的命名空间
namespace Article;
?>

It should be noted that there cannot be any code in front of the first namespace of the current script file. The following writing methods are Wrong:

Example 1

//在脚本前面写了一些逻辑代码
<?php
$path = "/";
class Comment { }
namespace Article;
?>

Example 2

</html>
<?php
namespace Article;
?>

Why do you want to say the first namespace? Because multiple namespaces can be created in the same script file.

Below I created two namespaces, and added a Comment class element to each of these two spaces:

<?php
//创建一个名为&#39;Article&#39;的命名空间
namespace Article;
//此Comment属于Article空间的元素
class Comment {
}
//创建一个名为&#39;MessageBoard&#39;的命名空间
namespace MessageBoard;
//此Comment属于MessageBoard空间的元素
class Comment {
}
?>

You cannot directly call other elements between different spaces, you need to use Namespace syntax:

<?php
namespace Article;
class Comment {
}
namespace MessageBoard;
class Comment {
}
//调用当前空间（MessageBoard）的Comment类
$comment = new Comment();
//调用Article空间的Comment类
$article_comment = new \Article\Comment();
?>

You can see that when calling the Comment class in the article space in the MessageBoard space, a file path-like syntax is used: \space name\element name

Except for classes, the usage of functions and constants is the same. Below I create new elements for the two spaces and output their values ​​in the MessageBoard space.

<?php
namespace Article;
const PATH = &#39;/article&#39;;
function getCommentTotal() {
	return 100;
}
class Comment {
}
namespace MessageBoard;
const PATH = &#39;/message_board&#39;;
function getCommentTotal() {
	return 300;
}
class Comment {
}
//调用当前空间的常量、函数和类
echo PATH;
///message_board
echo getCommentTotal();
//300
$comment = new Comment();
//调用Article空间的常量、函数和类
echo \Article\PATH;
///article
echo \Article\getCommentTotal();
//100
$article_comment = new \Article\Comment();
?>

Then I did get the element data of the Article space.

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