PHP Namespaces
PHP Namespaces
Namespaces are qualifiers that solve two different problems:
- They allow for better organization by grouping classes that work together to perform a task
- They allow the same name to be used for more than one class
For example, you may have a set of classes which describe an HTML table, such as Table, Row and Cell while also having another set of classes to describe furniture, such as Table, Chair and Bed. Namespaces can be used to organize the classes into two different groups while also preventing the two classes Table and Table from being mixed up.
Declaring a Namespace
Namespaces are declared at the beginning of a file using the namespace keyword:
Syntax
Declare a namespace called Html:
namespace Html;
Note: A namespace declaration must be the first thing in the PHP file. The following code
would be invalid:
<?php
echo "Hello World!";
namespace Html;
...
?>
Constants, classes and functions declared in this file will belong to the Html namespace:
Example
Create a Table class in the Html namespace:
<?php
namespace Html;
class Table {
public $title = "";
public
$numRows = 0;
public function message() {
echo "<p>Table
'{$this->title}' has {$this->numRows} rows.</p>";
}
}
$table = new
Table();
$table->title = "My table";
$table->numRows = 5;
?>
<!DOCTYPE html>
<html>
<body>
<?php
$table->message();
?>
</body>
</html>
Try it Yourself »
For further organization, it is possible to have nested namespaces:
Syntax
Declare a namespace called Html inside a namespace called Code:
namespace Code\Html;
Using Namespaces
Any code that follows a namespace declaration is operating inside the namespace, so
classes that belong to the namespace can be instantiated without any qualifiers. To access
classes from outside a namespace, the class needs to have the namespace attached
to it.
Example
Use classes from the Html namespace:
$table = new Html\Table()
$row = new Html\Row();
Try it Yourself »
When many classes from the same namespace are being used at the same time, it is
easier to use the namespace keyword:
Example
Use classes from the Html namespace without the need for the Html\qualifier:
namespace Html;
$table = new Table();
$row = new Row();
Try it Yourself »
Namespace Alias
It can be useful to give a namespace or class an alias to make it easier to write. This is
done with the use keyword:
