namespaces.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<chapter xml:id="language.namespaces" xmlns="http://docbook.org/ns/docbook"
 version="1.1">
 <title>Namespaces</title>

 <sect1 xml:id="language.namespaces.rationale">
  <title>Namespaces overview</title>
  <titleabbrev>Overview</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <simpara>
   What are namespaces? In the broadest definition namespaces are a way of encapsulating
   items. This can be seen as an abstract concept in many places. For example, in any
   operating system directories serve to group related files, and act as a namespace for
   the files within them. As a concrete example, the file <literal>foo.txt</literal> can
   exist in both directory <literal>/home/greg</literal> and in <literal>/home/other</literal>,
   but two copies of <literal>foo.txt</literal> cannot co-exist in the same directory. In
   addition, to access the <literal>foo.txt</literal> file outside of the
   <literal>/home/greg</literal> directory, we must prepend the directory name to the file
   name using the directory separator to get <literal>/home/greg/foo.txt</literal>. This
   same principle extends to namespaces in the programming world.
  </simpara>

  <simpara>
   In the PHP world, namespaces are designed to solve two problems that authors
   of libraries and applications encounter when creating re-usable code elements
   such as classes or functions:
  </simpara>
  <para>
   <orderedlist>
    <listitem>
     <simpara>
      Name collisions between code you create, and
      internal PHP classes/functions/constants or third-party classes/functions/constants.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      Ability to alias (or shorten) Extra_Long_Names designed to alleviate the first problem,
      improving readability of source code.
     </simpara>
    </listitem>
   </orderedlist>
  </para>
  <simpara>
   PHP Namespaces provide a way in which to group related classes, interfaces,
   functions and constants. Here is an example of namespace syntax in PHP:
  </simpara>
  <example>
   <title>Namespace syntax example</title>
   <programlisting role="php">
   <![CDATA[
<?php
namespace my\name; // see "Defining Namespaces" section

class MyClass {}
function myfunction() {}
const MYCONST = 1;

$a = new MyClass;
$c = new \my\name\MyClass; // see "Global Space" section

$a = strlen('hi'); // see "Using namespaces: fallback to global
                   // function/constant" section

$d = namespace\MYCONST; // see "namespace operator and __NAMESPACE__
                        // constant" section
$d = __NAMESPACE__ . '\MYCONST';
echo constant($d); // see "Namespaces and dynamic language features" section
?>
    ]]>
   </programlisting>
  </example>
   <note>
    <simpara>
     Namespace names are case-insensitive.
    </simpara>
   </note>
  <note>
   <para>
    The Namespace name <literal>PHP</literal>, and compound names starting
    with this name (like <literal>PHP\Classes</literal>) are reserved for internal language use
    and should not be used in the userspace code.
   </para>
  </note>
 </sect1>

 <sect1 xml:id="language.namespaces.definition">
  <title>Defining namespaces</title>
  <titleabbrev>Namespaces</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <para>
   Although any valid PHP code can be contained within a namespace, only the following
   types of code are affected by namespaces: classes (including abstract classes, traits and enums), interfaces,
   functions and constants.
  </para>
  <para>
   Namespaces are declared using the <literal>namespace</literal>
   keyword. A file containing a namespace must declare the namespace
   at the top of the file before any other code - with one exception: the
   <xref linkend="control-structures.declare" /> keyword.
   <example>
    <title>Declaring a single namespace</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace MyProject;

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

?>
]]>
    </programlisting>
   </example>
   <note>
    <simpara>
     Fully qualified names (i.e. names starting with a backslash) are not allowed in namespace
     declarations, because such constructs are interpreted as relative namespace expressions.
    </simpara>
   </note>
   The only code construct allowed before a namespace declaration is the
   <literal>declare</literal> statement, for defining encoding of a source file. In addition,
   no non-PHP code may precede a namespace declaration, including extra whitespace:
   <example>
    <title>Declaring a single namespace</title>
    <programlisting role="php">
     <![CDATA[
<html>
<?php
namespace MyProject; // fatal error - namespace must be the first statement in the script
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   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.
  </para>
 </sect1>
 <sect1 xml:id="language.namespaces.nested">
  <title>Declaring sub-namespaces</title>
  <titleabbrev>Sub-namespaces</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <para>
   Much like directories and files, PHP namespaces also contain the ability to specify
   a hierarchy of namespace names. Thus, a namespace name can be defined with
   sub-levels:
   <example>
    <title>Declaring a single namespace with hierarchy</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace MyProject\Sub\Level;

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

?>
]]>
    </programlisting>
   </example>
   The above example creates constant <literal>MyProject\Sub\Level\CONNECT_OK</literal>,
   class <literal>MyProject\Sub\Level\Connection</literal> and function
   <literal>MyProject\Sub\Level\connect</literal>.
  </para>
 </sect1>
 <sect1 xml:id="language.namespaces.definitionmultiple">
  <title>Defining multiple namespaces in the same file</title>
  <titleabbrev>Defining multiple namespaces in the same file</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <para>
   Multiple namespaces may also be declared in the same file. There are two allowed
   syntaxes.
  </para>
  <para>
   <example>
    <title>Declaring multiple namespaces, simple combination syntax</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace MyProject;

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

namespace AnotherProject;

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   This syntax is not recommended for combining namespaces into a single file.
   Instead it is recommended to use the alternate bracketed syntax.
  </para>
  <para>
   <example>
    <title>Declaring multiple namespaces, bracketed syntax</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace MyProject {

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

namespace AnotherProject {

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   It is strongly discouraged as a coding practice to combine multiple namespaces into
   the same file. The primary use case is to combine multiple PHP scripts into the same
   file.
  </para>
  <para>
   To combine global non-namespaced code with namespaced code, only bracketed syntax is
   supported. Global code should be
   encased in a namespace statement with no namespace name as in:
   <example>
    <title>Declaring multiple namespaces and unnamespaced code</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace MyProject {

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

namespace { // global code
session_start();
$a = MyProject\connect();
echo MyProject\Connection::start();
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   No PHP code may exist outside of the namespace brackets except for an opening
   declare statement.
   <example>
    <title>Declaring multiple namespaces and unnamespaced code</title>
    <programlisting role="php">
     <![CDATA[
<?php
declare(encoding='UTF-8');
namespace MyProject {

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

namespace { // global code
session_start();
$a = MyProject\connect();
echo MyProject\Connection::start();
}
?>
]]>
    </programlisting>
   </example>
  </para>
 </sect1>
 <sect1 xml:id="language.namespaces.basics">
  <title>Using namespaces: Basics</title>
  <titleabbrev>Basics</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <para>
   Before discussing the use of namespaces, it is important to understand how PHP
   knows which namespaced element your code is requesting. A simple analogy can be made
   between PHP namespaces and a filesystem. There are three ways to access a file in a
   file system:
   <orderedlist>
    <listitem>
     <simpara>
      Relative file name like <literal>foo.txt</literal>. This resolves to
      <literal>currentdirectory/foo.txt</literal> where <literal>currentdirectory</literal> is the
      directory currently occupied. So if the current directory is
      <literal>/home/foo</literal>, the name resolves to <literal>/home/foo/foo.txt</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      Relative path name like <literal>subdirectory/foo.txt</literal>. This resolves
      to <literal>currentdirectory/subdirectory/foo.txt</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      Absolute path name like <literal>/main/foo.txt</literal>. This resolves
      to <literal>/main/foo.txt</literal>.
     </simpara>
    </listitem>
   </orderedlist>
   The same principle can be applied to namespaced elements in PHP. For
   example, a class name can be referred to in three ways:
   <orderedlist>
    <listitem>
     <simpara>
      Unqualified name, or an unprefixed class name like
      <literal>$a = new foo();</literal> or
      <literal>foo::staticmethod();</literal>. If the current namespace is
      <literal>currentnamespace</literal>, this resolves to
      <literal>currentnamespace\foo</literal>. If
      the code is global, non-namespaced code, this resolves to <literal>foo</literal>.
     </simpara>
     <simpara>
      One caveat: unqualified names for functions and constants will
      resolve to global functions and constants if the namespaced function or constant
      is not defined. See <link linkend="language.namespaces.fallback">Using namespaces:
      fallback to global function/constant</link> for details.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      Qualified name, or a prefixed class name like
      <literal>$a = new subnamespace\foo();</literal> or
      <literal>subnamespace\foo::staticmethod();</literal>. If the current namespace is
      <literal>currentnamespace</literal>, this resolves to
      <literal>currentnamespace\subnamespace\foo</literal>. If
      the code is global, non-namespaced code, this resolves to <literal>subnamespace\foo</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      Fully qualified name, or a prefixed name with global prefix operator like
      <literal>$a = new \currentnamespace\foo();</literal> or
      <literal>\currentnamespace\foo::staticmethod();</literal>. This always resolves
      to the literal name specified in the code, <literal>currentnamespace\foo</literal>.
     </simpara>
    </listitem>
   </orderedlist>
  </para>
  <para>
   Here is an example of the three kinds of syntax in actual code:
   <informalexample>
    <simpara>file1.php</simpara>
    <programlisting role="php">
     <![CDATA[
<?php
namespace Foo\Bar\subnamespace;

const FOO = 1;
function foo() {}
class foo
{
    static function staticmethod() {}
}
?>
     ]]>
    </programlisting>
    <simpara>file2.php</simpara>
    <programlisting role="php">
     <![CDATA[
<?php
namespace Foo\Bar;
include 'file1.php';

const FOO = 2;
function foo() {}
class foo
{
    static function staticmethod() {}
}

/* Unqualified name */
foo(); // resolves to function Foo\Bar\foo
foo::staticmethod(); // resolves to class Foo\Bar\foo, method staticmethod
echo FOO; // resolves to constant Foo\Bar\FOO

/* Qualified name */
subnamespace\foo(); // resolves to function Foo\Bar\subnamespace\foo
subnamespace\foo::staticmethod(); // resolves to class Foo\Bar\subnamespace\foo,
                                  // method staticmethod
echo subnamespace\FOO; // resolves to constant Foo\Bar\subnamespace\FOO

/* Fully qualified name */
\Foo\Bar\foo(); // resolves to function Foo\Bar\foo
\Foo\Bar\foo::staticmethod(); // resolves to class Foo\Bar\foo, method staticmethod
echo \Foo\Bar\FOO; // resolves to constant Foo\Bar\FOO
?>
     ]]>
    </programlisting>
   </informalexample>
  </para>
  <para>
   Note that to access any global
   class, function or constant, a fully qualified name can be used, such as
   <function>\strlen</function> or <classname>\Exception</classname> or
   \<constant>INI_ALL</constant>.
   <example>
    <title>Accessing global classes, functions and constants from within a namespace</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace Foo;

function strlen() {}
const INI_ALL = 3;
class Exception {}

$a = \strlen('hi'); // calls global function strlen
$b = \INI_ALL; // accesses global constant INI_ALL
$c = new \Exception('error'); // instantiates global class Exception
?>
     ]]>
    </programlisting>
   </example>
  </para>
 </sect1>
 <sect1 xml:id="language.namespaces.dynamic">
  <title>Namespaces and dynamic language features</title>
  <titleabbrev>Namespaces and dynamic language features</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <para>
   PHP's implementation of namespaces is influenced by its dynamic nature as a programming
   language. Thus, to convert code like the following example into namespaced code:
   <example>
    <title>Dynamically accessing elements</title>
    <simpara>example1.php:</simpara>
    <programlisting role="php">
     <![CDATA[
<?php
class classname
{
    function __construct()
    {
        echo __METHOD__,"\n";
    }
}
function funcname()
{
    echo __FUNCTION__,"\n";
}
const constname = "global";

$a = 'classname';
$obj = new $a; // prints classname::__construct
$b = 'funcname';
$b(); // prints funcname
echo constant('constname'), "\n"; // prints global
?>
    ]]>
    </programlisting>
   </example>
   One must use the fully qualified name (class name with namespace prefix).
   Note that because there is no difference between a qualified and a fully qualified Name
   inside a dynamic class name, function name, or constant name, the leading backslash is
   not necessary.
   <example>
    <title>Dynamically accessing namespaced elements</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace namespacename;
class classname
{
    function __construct()
    {
        echo __METHOD__,"\n";
    }
}
function funcname()
{
    echo __FUNCTION__,"\n";
}
const constname = "namespaced";

/* note that if using double quotes, "\\namespacename\\classname" must be used */
$a = '\namespacename\classname';
$obj = new $a; // prints namespacename\classname::__construct
$a = 'namespacename\classname';
$obj = new $a; // also prints namespacename\classname::__construct
$b = 'namespacename\funcname';
$b(); // prints namespacename\funcname
$b = '\namespacename\funcname';
$b(); // also prints namespacename\funcname
echo constant('\namespacename\constname'), "\n"; // prints namespaced
echo constant('namespacename\constname'), "\n"; // also prints namespaced
?>
    ]]>
    </programlisting>
   </example>
  </para>
  <para>
   Be sure to read the <link linkend="language.namespaces.faq.quote">note about
   escaping namespace names in strings</link>.
  </para>
 </sect1>
 <sect1 xml:id="language.namespaces.nsconstants">
  <title>The namespace keyword and __NAMESPACE__ magic constant</title>
  <titleabbrev>namespace keyword and __NAMESPACE__</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <para>
   PHP supports two ways of abstractly accessing elements within the current namespace,
   the <constant>__NAMESPACE__</constant> magic constant, and the <literal>namespace</literal>
   keyword.
  </para>
  <para>
   The value of <constant>__NAMESPACE__</constant> is a string that contains the current
   namespace name. In global, un-namespaced code, it contains an empty string.
   <example>
    <title>__NAMESPACE__ example, namespaced code</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace MyProject;

echo '"', __NAMESPACE__, '"'; // outputs "MyProject"
?>
]]>
    </programlisting>
   </example>
   <example>
    <title>__NAMESPACE__ example, global code</title>
    <programlisting role="php">
     <![CDATA[
<?php

echo '"', __NAMESPACE__, '"'; // outputs ""
?>
]]>
    </programlisting>
   </example>
   The <constant>__NAMESPACE__</constant> constant is useful for dynamically constructing
   names, for instance:
   <example>
    <title>using __NAMESPACE__ for dynamic name construction</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace MyProject;

function get($classname)
{
    $a = __NAMESPACE__ . '\\' . $classname;
    return new $a;
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   The <literal>namespace</literal> keyword can be used to explicitly request
   an element from the current namespace or a sub-namespace. It is the namespace
   equivalent of the <literal>self</literal> operator for classes.
   <example>
    <title>the namespace operator, inside a namespace</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace MyProject;

use blah\blah as mine; // see "Using namespaces: Aliasing/Importing"

blah\mine(); // calls function MyProject\blah\mine()
namespace\blah\mine(); // calls function MyProject\blah\mine()

namespace\func(); // calls function MyProject\func()
namespace\sub\func(); // calls function MyProject\sub\func()
namespace\cname::method(); // calls static method "method" of class MyProject\cname
$a = new namespace\sub\cname(); // instantiates object of class MyProject\sub\cname
$b = namespace\CONSTANT; // assigns value of constant MyProject\CONSTANT to $b
?>
]]>
    </programlisting>
   </example>
   <example>
    <title>the namespace operator, in global code</title>
    <programlisting role="php">
     <![CDATA[
<?php

namespace\func(); // calls function func()
namespace\sub\func(); // calls function sub\func()
namespace\cname::method(); // calls static method "method" of class cname
$a = new namespace\sub\cname(); // instantiates object of class sub\cname
$b = namespace\CONSTANT; // assigns value of constant CONSTANT to $b
?>
]]>
    </programlisting>
   </example>
  </para>
 </sect1>

 <sect1 xml:id="language.namespaces.importing">
  <title>Using namespaces: Aliasing/Importing</title>
  <titleabbrev>Aliasing and Importing</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <para>
   The ability to refer to an external fully qualified name with an alias, or importing,
   is an important feature of namespaces. This is similar to the
   ability of unix-based filesystems to create symbolic links to a file or to a directory.
  </para>
  <para>
   PHP can alias(/import) constants, functions, classes, interfaces, traits, enums and namespaces.
  </para>
  <para>
   Aliasing is accomplished with the <literal>use</literal> operator.
   Here is an example showing all 5 kinds of importing:
   <example>
    <title>importing/aliasing with the use operator</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace foo;
use My\Full\Classname as Another;

// this is the same as use My\Full\NSname as NSname
use My\Full\NSname;

// importing a global class
use ArrayObject;

// importing a function
use function My\Full\functionName;

// aliasing a function
use function My\Full\functionName as func;

// importing a constant
use const My\Full\CONSTANT;

$obj = new namespace\Another; // instantiates object of class foo\Another
$obj = new Another; // instantiates object of class My\Full\Classname
NSname\subns\func(); // calls function My\Full\NSname\subns\func
$a = new ArrayObject(array(1)); // instantiates object of class ArrayObject
// without the "use ArrayObject" we would instantiate an object of class foo\ArrayObject
func(); // calls function My\Full\functionName
echo CONSTANT; // echoes the value of My\Full\CONSTANT
?>
]]>
    </programlisting>
   </example>
   Note that for namespaced names (fully qualified namespace names containing
   namespace separator, such as <literal>Foo\Bar</literal> as opposed to global names that
   do not, such as <literal>FooBar</literal>), the leading backslash is unnecessary and not
   recommended, as import names
   must be fully qualified, and are not processed relative to the current namespace.
  </para>
  <para>
   PHP additionally supports a convenience shortcut to place multiple use statements
   on the same line
   <example>
    <title>importing/aliasing with the use operator, multiple use statements combined</title>
    <programlisting role="php">
     <![CDATA[
<?php
use My\Full\Classname as Another, My\Full\NSname;

$obj = new Another; // instantiates object of class My\Full\Classname
NSname\subns\func(); // calls function My\Full\NSname\subns\func
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   Importing is performed at compile-time, and so does not affect dynamic class, function
   or constant names.
   <example>
    <title>Importing and dynamic names</title>
    <programlisting role="php">
     <![CDATA[
<?php
use My\Full\Classname as Another, My\Full\NSname;

$obj = new Another; // instantiates object of class My\Full\Classname
$a = 'Another';
$obj = new $a;      // instantiates object of class Another
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   In addition, importing only affects unqualified and qualified names. Fully qualified
   names are absolute, and unaffected by imports.
   <example>
    <title>Importing and fully qualified names</title>
    <programlisting role="php">
     <![CDATA[
<?php
use My\Full\Classname as Another, My\Full\NSname;

$obj = new Another; // instantiates object of class My\Full\Classname
$obj = new \Another; // instantiates object of class Another
$obj = new Another\thing; // instantiates object of class My\Full\Classname\thing
$obj = new \Another\thing; // instantiates object of class Another\thing
?>
]]>
    </programlisting>
   </example>
  </para>
  <sect2 xml:id="language.namespaces.importing.scope">
   <title>Scoping rules for importing</title>
   <para>
    The <literal>use</literal> keyword must be declared in the
    outermost scope of a file (the global scope) or inside namespace
    declarations. This is because the importing is done at compile
    time and not runtime, so it cannot be block scoped. The following
    example will show an illegal use of the <literal>use</literal>
    keyword:
   </para>
   <para>
    <example>
     <title>Illegal importing rule</title>
     <programlisting role="php">
<![CDATA[
<?php
namespace Languages;

function toGreenlandic()
{
    use Languages\Danish;

    // ...
}
?>
]]>
     </programlisting>
    </example>
   </para>
   <note>
    <para>
     Importing rules are per file basis, meaning included files will
     <emphasis>NOT</emphasis> inherit the parent file's importing rules.
    </para>
   </note>
  </sect2>
  <sect2 xml:id="language.namespaces.importing.group">
   <title>Group <literal>use</literal> declarations</title>
   <para>
    Classes, functions and constants being imported from
    the same &namespace; can be grouped together in a single &use.namespace;
    statement.
   </para>
   <informalexample>
    <programlisting role="php">
<![CDATA[
<?php

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;

// is equivalent to the following groupped use declaration
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};
]]>
    </programlisting>
   </informalexample>
  </sect2>
 </sect1>
 <sect1 xml:id="language.namespaces.global">
  <title>Global space</title>
  <titleabbrev>Global space</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <para>
   Without any namespace definition, all class and function definitions are
   placed into the global space - as it was in PHP before namespaces were
   supported. Prefixing a name with <literal>\</literal> will specify that
   the name is required from the global space even in the context of the
   namespace.
   <example>
    <title>Using global space specification</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace A\B\C;

/* This function is A\B\C\fopen */
function fopen() {
     /* ... */
     $f = \fopen(...); // call global fopen
     return $f;
}
?>
    ]]>
    </programlisting>
   </example>
  </para>
 </sect1>
 <sect1 xml:id="language.namespaces.fallback">
  <title>Using namespaces: fallback to the global space for functions and constants</title>
  <titleabbrev>Fallback to global space</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <para>
   Inside a namespace, when PHP encounters an unqualified Name in a class name, function or
   constant context, it resolves these with different priorities. Class names always
   resolve to the current namespace name. Thus to access internal or non-namespaced
   user classes, one must refer to them with their fully qualified Name as in:
   <example>
    <title>Accessing global classes inside a namespace</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace A\B\C;
class Exception extends \Exception {}

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

$c = new ArrayObject; // fatal error, class A\B\C\ArrayObject not found
?>
    ]]>
    </programlisting>
   </example>
  </para>
  <para>
   For functions and constants, PHP will fall back to global functions or constants
   if a namespaced function or constant does not exist.
   <example>
    <title>global functions/constants fallback inside a namespace</title>
    <programlisting role="php">
     <![CDATA[
<?php
namespace A\B\C;

const E_ERROR = 45;
function strlen($str)
{
    return \strlen($str) - 1;
}

echo E_ERROR, "\n"; // prints "45"
echo INI_ALL, "\n"; // prints "7" - falls back to global INI_ALL

echo strlen('hi'), "\n"; // prints "1"
if (is_array('hi')) { // prints "is not array"
    echo "is array\n";
} else {
    echo "is not array\n";
}
?>
    ]]>
    </programlisting>
   </example>
  </para>
 </sect1>

 <sect1 xml:id="language.namespaces.rules">
  <title>Name resolution rules</title>
  <titleabbrev>Name resolution rules</titleabbrev>
  <?phpdoc print-version-for="namespaces"?>
  <para>
   For the purposes of these resolution rules, here are some important definitions:
   <variablelist>
    <title>Namespace name definitions</title>
    <varlistentry>
     <term>Unqualified name</term>
     <listitem>
      <para>
       This is an identifier without a namespace separator, such as <literal>Foo</literal>
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>Qualified name</term>
     <listitem>
      <para>
       This is an identifier with a namespace separator, such as <literal>Foo\Bar</literal>
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>Fully qualified name</term>
     <listitem>
      <para>
       This is an identifier with a namespace separator that begins with a
       namespace separator, such as <literal>\Foo\Bar</literal>. The namespace
       <literal>\Foo</literal> is also a fully qualified name.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>Relative name</term>
     <listitem>
      <para>
       This is an identifier starting with <literal>namespace</literal>, such as
       <literal>namespace\Foo\Bar</literal>.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
  <para>
   Names are resolved following these resolution rules:
   <orderedlist>
    <listitem>
     <simpara>
      Fully qualified names always resolve to the name without leading namespace separator.
      For instance <literal>\A\B</literal> resolves to <literal>A\B</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      Relative names always resolve to the name with <literal>namespace</literal> replaced by
      the current namespace. If the name occurs in the global namespace, the
      <literal>namespace\</literal> prefix is stripped. For example <literal>namespace\A</literal>
      inside namespace <literal>X\Y</literal> resolves to <literal>X\Y\A</literal>. The same name
      inside the global namespace resolves to <literal>A</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      For qualified names the first segment of the name is translated according to the current
      class/namespace import table. For example, if the namespace <literal>A\B\C</literal> is
      imported as <literal>C</literal>, the name <literal>C\D\E</literal> is translated to
      <literal>A\B\C\D\E</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      For qualified names, if no import rule applies, the current namespace is prepended to the
      name. For example, the name <literal>C\D\E</literal> inside namespace <literal>A\B</literal>,
      resolves to <literal>A\B\C\D\E</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      For unqualified names, the name is translated according to the current import table for the
      respective symbol type. This means that class-like names are translated according to the
      class/namespace import table, function names according to the function import table and
      constants according to the constant import table. For example, after
      <literal>use A\B\C;</literal> a usage such as <literal>new C()</literal> resolves to the name
      <literal>A\B\C()</literal>. Similarly, after <literal>use function A\B\foo;</literal> a usage
      such as <literal>foo()</literal> resolves to the name <literal>A\B\foo</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      For unqualified names, if no import rule applies and the name refers to a class-like symbol,
      the current namespace is prepended. For example <literal>new C()</literal> inside namespace
      <literal>A\B</literal> resolves to name <literal>A\B\C</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      For unqualified names, if no import rule applies and the name refers to a function or constant
      and the code is outside the global namespace, the name is resolved at runtime.
      Assuming the code is in namespace <literal>A\B</literal>, here is how a call to function
      <literal>foo()</literal> is resolved:
     </simpara>
      <orderedlist>
       <listitem>
        <simpara>
         It looks for a function from the current namespace:
         <literal>A\B\foo()</literal>.
        </simpara>
       </listitem>
       <listitem>
        <simpara>
         It tries to find and call the <emphasis>global</emphasis> function
         <literal>foo()</literal>.
        </simpara>
       </listitem>
      </orderedlist>
    </listitem>
   </orderedlist>
  </para>
  <example>
   <title>Name resolutions illustrated</title>
   <programlisting role="php">
<![CDATA[
<?php
namespace A;