PHP - Manual: 定义命名空间

2024-12-23

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« 命名空间概述

定义命名空间

(PHP 5 >= 5.3.0, PHP 7, PHP 8)

虽然任意合法的 PHP 代码都可以包含在命名空间中，但只有以下类型的代码受命名空间的影响，它们是：类（包括抽象类和 trait）、接口、函数和常量。

命名空间通过关键字 namespace 来声明。如果一个文件中包含命名空间，它必须在其它所有代码之前声明命名空间，除了一个以外：declare关键字。

示例 #1 声明单个命名空间


<?php
namespace MyProject;

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }

?>

注意: 完全限定名称（就是以反斜杠开头的名称）不能用于命名空间的声明。因为该结构会解析成相对命名空间表达式。

在声明命名空间之前唯一合法的代码是用于定义源文件编码方式的 declare 语句。另外，所有非 PHP 代码包括空白符都不能出现在命名空间的声明之前：

示例 #2 声明单个命名空间


<html>
<?php
namespace MyProject; // 致命错误 -　命名空间必须是程序脚本的第一条语句
?>

另外，与 PHP 其它的语言特征不同，同一个命名空间可以定义在多个文件中，即允许将同一个命名空间的内容分割存放在不同的文件中。

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User Contributed Notes 9 notes

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191

kuzawinski dot marcin at NOSPAM dot gmail dot com ¶

7 years ago


If your code looks like this:

<?php
    namespace NS;
?>

...and you still get "Namespace declaration statement has to be the very first statement in the script" Fatal error, then you probably use UTF-8 encoding (which is good) with Byte Order Mark, aka BOM (which is bad). Try to convert your files to "UTF-8 without BOM", and it should be ok.

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136

danbettles at yahoo dot co dot uk ¶

13 years ago


Regarding constants defined with define() inside namespaces...

define() will define constants exactly as specified.  So, if you want to define a constant in a namespace, you will need to specify the namespace in your call to define(), even if you're calling define() from within a namespace.  The following examples will make it clear.

The following code will define the constant "MESSAGE" in the global namespace (i.e. "\MESSAGE").

<?php
namespace test;
define('MESSAGE', 'Hello world!');
?>

The following code will define two constants in the "test" namespace.

<?php
namespace test;
define('test\HELLO', 'Hello world!');
define(__NAMESPACE__ . '\GOODBYE', 'Goodbye cruel world!');
?>

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FatBat ¶

8 years ago


Expanding on @danbettles note, it is better to always be explicit about which constant to use.

<?php
    namespace NS;

    define(__NAMESPACE__ .'\foo','111');
    define('foo','222');

    echo foo;  // 111.
    echo \foo;  // 222.
    echo \NS\foo  // 111.
    echo NS\foo  // fatal error. assumes \NS\NS\foo.
?>

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huskyr at gmail dot com ¶

12 years ago


"A file containing a namespace must declare the namespace at the top of the file before any other code"


It might be obvious, but this means that you *can* include comments and white spaces before the namespace keyword.


<?php

// Lots 

// of

// interesting

// comments and white space


namespace Foo;

class Bar {

}

?>

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jeremeamia at gmail dot com ¶

12 years ago


You should not try to create namespaces that use PHP keywords. These will cause parse errors. 


Examples:


<?php

namespace Project/Classes/Function; // Causes parse errors

namespace Project/Abstract/Factory; // Causes parse errors

?>

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anisgazig at gmail dot com ¶

1 year ago


namespace statement  is defined at first of the php files. But 
    before namespace declaration only three elements allowed.
      1.declare statement
      2.spaces
      3.comments

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Anonymous ¶

14 years ago


@ RS: Also, you can specify how your __autoload() function looks for the files. That way another users namespace classes cannot overwrite yours unless they replace your file specifically.

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Baptiste ¶

14 years ago


There is nothing wrong with PHP namespaces, except that those 2 instructions give a false impression of package management.
... while they just correspond to the "with()" instruction of Javascript.

By contrast, a package is a namespace for its members, but it offers more (like deployment facilities), and a compiler knows exactly what classes are in a package, and where to find them.

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-1

anisgazig at gmail dot com ¶

1 year ago


Namespace name are case-insensitive.
namespace App
and
namespace app
are same meaning.

Besides, Namespace keword are case-insensitive.
Namespace App
namespace App
and
NAMESPACE App
are same meaning.

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官方地址：https://www.php.net/manual/en/language.namespaces.definition.php

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定义命名空间

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