Zend PHP 7 Certification – Basics – Namespaces

23rd August 2017

This post covers the Namespaces section of the PHP Basics chapter when studying for the Zend PHP 7 Certification.

Namespaces are a method of grouping related PHP code elements within a library or application.

Namespaces are use to solve a couple of problems including naming collisions, which most likely occur when code from multiple people is included in a project. For example, you could create a class or method that has exactly the same name as someone else’s class or method.

Although any valid PHP code can be contained within a namespace, only the following types of code are affected by namespaces:

Classes, including abstracts and traits.
Interfaces
Functions
Constants

Aside from the one exception of using the declare keyword, a file containing a namespace must declare the namespace at the top of the file before any other code.

<?php
namespace test;

const SOME_CONST = 1;
class someClass { ... }
function someFunc { ... }

A namespace name can also be defined with sub-levels.

<?php
namespace MyProject\Sub\Level;

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }

The above example creates constant MyProject\Sub\Level\CONNECT_OK, class MyProject\Sub\Level\Connection and function MyProject\Sub\Level\connect.

Unless a namespace is defined, classes and functions are declared within the global scope.

It is strongly discouraged as a coding practice to combine multiple namespaces into the same file. However, if you need to then use bracketed syntax:

<?php
namespace MyProject {

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }
}

namespace AnotherProject {

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }
}

As seen in the constants chapter, the __NAMESPACE__ magic constant contains the current namespace.

<?php
namespace somenamespace;

echo __NAMESPACE__; // Outputs: somenamespace

Namespaces can be imported with the use operator. Note that you can also alias the namespace by using the as keyword.

<?php
namespace foo;

use My\Full\Classname as Another;

Without any namespace definition, all class and function definitions are placed into the global space. Prefixing a name with \ will specify that the name is required from the global space even in the context of the namespace.

<?php
namespace A\B\C;

class Exception extends \Exception {}

$a = new Exception('Some exception'); // $a is an object of class A\B\C\Exception
$b = new \Exception('Some exception'); // $b is an object of class Exception

As of PHP 7.0, classes, functions and constants being imported from the same namespace can be grouped together in a single use statement.

<?php
// Pre PHP 7 code
use some\namespace\ClassA;
use some\namespace\ClassB;
use some\namespace\ClassC as C;

use function some\namespace\fn_a;
use function some\namespace\fn_b;
use function some\namespace\fn_c;

use const some\namespace\ConstA;
use const some\namespace\ConstB;
use const some\namespace\ConstC;

// PHP 7+ code
use some\namespace\{ClassA, ClassB, ClassC as C};
use function some\namespace\{fn_a, fn_b, fn_c};
use const some\namespace\{ConstA, ConstB, ConstC};

View the other sections:

Note: This article is based on PHP version 7.0.