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Dokumen ini menggunakan Manual laman web PHP Cina Lepaskan
(PHP 5 >= 5.3.0)
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traits)、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。
Example #1 声明单个命名空间
<?php
namespace MyProject ;
const CONNECT_OK = 1 ;
class Connection { }
function connect () { }
?>
Example #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。
[#1] kuzawinski dot marcin at NOSPAM dot gmail dot com [2014-08-05 21:52:02]
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.
[#2] Roadowl [2014-02-24 23:42:00]
quote:
Defining namespaces
(...)
Namespaces are declared using the namespace keyword. A file containing a namespace must declare the namespace at the top of the file before any other code - with one exception: the declare keyword.
end quote.
So we have a title that talks 'defining' and a piece of text that talks 'declare' three times, one of which could be referring to some other 'declare' than the former two.
Please, documentation authors -- get your act together, finally.
[#3] FatBat [2013-08-08 21:46:33]
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.
?>
[#4] huskyr at gmail dot com [2009-10-05 04:20:48]
"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 {
}
?>
[#5] jeremeamia at gmail dot com [2009-07-14 08:43:55]
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
?>
[#6] danbettles at yahoo dot co dot uk [2009-04-14 12:02:21]
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!');
?>
[#7] David Drakard [2008-09-07 05:56:02]
I agree with SR, the new namespaces feature has solved a number of problems for me which would have required horrible coding to solve otherwise.
An example use:
Say you are making a small script, and write a class to connect to a database, calling it 'connection'. If you find your script useful and gradually expand it into a large application, you may want to rename the class. Without namespaces, you have to change the name and every reference to it (say in inheriting objects), possibly creating a load of bugs. With namespaces you can drop the related classes into a namespace with one line of code, and less chance of errors.
This is by no means one of the biggest problems namespaces solve; I would suggest reading about their advantages before citicising them. They provide an elegant solutions to several problems involved in creating complex systems.
[#8] Baptiste [2008-05-14 12:47:03]
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.
[#9] Anonymous [2008-04-01 11:11:34]
@ 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.