Although any valid PHP code can be contained within a namespace, only three type of code are affected by namespaces: classes, functions and constants.
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.
Example #1 Declaring a single namespace
The only code construct allowed before a namespace declaration is the declare statement, for defining encoding of a source file. In addition, no non-PHP code may precede a namespace declaration, including extra whitespace:
Example #2 Declaring a single namespace
In addition, unlike any other PHP construct, the same namespace may be defined in multiple files, allowing splitting up of a namespace’s contents across the filesystem.
Huskyr at gmail dot com 05-Oct-2009 11:20
“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.
Jeremeamia at gmail dot com 14-Jul-2009 03:43
You should not try to create namespaces that use PHP keywords. These will cause parse errors.
Danbettles at yahoo dot co dot uk 14-Apr-2009 07:02
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”).
The following code will define two constants in the “test” namespace.
Drakard 07-Sep-2008 12:56
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.
Baptiste 14-May-2008 07:47
There is nothing wrong with PHP namespaces, except that those 2 instructions give a false impression of package management.
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.
Anonymous 01-Apr-2008 07:11
@ 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.