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7.13 PHP Namespaces

Namespaces are qualifiers that solve two different problems:
1. They allow for better organization by grouping classes that work together to perform a task
2. 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 1: PHP Namespaces - Declaring a Namespace

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>

For further organization, it is possible to have nested namespaces:

Syntax

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 2: PHP Namespaces - Using Namespaces part 1

Use classes from the Html namespace:

$table = new Html\Table()
$row = new Html\Row();

When many classes from the same namespace are being used at the same time, it is easier to use the namespace keyword:

Example 3: PHP Namespaces - Using Namespaces part 2

Use classes from the Html namespace without the need for the Html\qualifier:

namespace Html;
$table = new Table();
$row = new Row();

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:

Example 4: PHP Namespaces - Namespace Alias part 1

Give a namespace an alias:

use Html as H;
$table = new H\Table();

Give a class an alias:

Example 5: PHP Namespaces - Namespace Alias part 2

Give a class an alias:

use Html\Table as T;
$table = new T();

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PHP Classes/Objects - Define a Class PHP Classes/Objects - Define Objects part 1 PHP Classes/Objects - Define Objects part 2 PHP Classes/Objects - The $this Keyword part 1 PHP Classes/Objects - The $this Keyword part 2 PHP Classes/Objects - instanceof PHP Constructor part 1 PHP Constructor part 2 PHP Destructor part 1 PHP Destructor part 2 PHP Access Modifiers part 1 PHP Access Modifiers part 2 PHP Inheritance PHP Inheritance - Inheritance and the Protected Access Modifier part 1 PHP Inheritance - Inheritance and the Protected Access Modifier part 2 PHP Inheritance - Overriding Inherited Methods PHP Inheritance - The final Keyword part 1 PHP Inheritance - The final Keyword part 2 PHP Class Constants part 1 PHP Class Constants part 2 PHP Abstract Classes part 1 PHP Abstract Classes part 2 PHP Abstract Classes part 3 PHP Interfaces - Using Interfaces part 1 PHP Interfaces - Using Interfaces part 2 PHP - Using Traits PHP - Using Multiple Traits PHP Static Methods part 1 PHP Static Methods part 2 PHP Static Methods part 3 PHP Static Methods part 4 PHP Static Properties part 1 PHP Static Properties part 2 PHP Static Properties part 3 menu Test (text file for navigating the site) Drop Down Menu PHP Namespaces - Declaring a Namespace PHP Namespaces - Using Namespaces part 1 PHP Namespaces - Using Namespaces part 2 PHP Namespaces - Namespace Alias part 1 PHP Namespaces - Namespace Alias part 2 PHP Iterables - Using Iterables part 1 PHP Iterables - Using Iterables part 2 PHP Iterables - Creating Iterables