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.
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() { /* ... */ }
?>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。
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 10 notes
kuzawinski dot marcin at NOSPAM dot gmail dot com ¶
10 years ago
danbettles at yahoo dot co dot uk ¶
15 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!');
?>
FatBat ¶
11 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.
?>
anisgazig at gmail dot com ¶
3 years 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
huskyr at gmail dot com ¶
15 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 {
}
?>
jeremeamia at gmail dot com ¶
15 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
?>
Anonymous ¶
16 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.
Baptiste ¶
16 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.
anisgazig at gmail dot com ¶
3 years 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.
dino at tuxweb dot it ¶
2 years ago
Please note that a PHP Namespace declaration cannot start with a number.
It took some time for me to debug...
