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<h2 class="title">Defining namespaces</h2>
<p class="verinfo">(PHP 5 >= 5.3.0)</p>
<p class="para">
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 and constants.
</p>
<p class="para">
Namespaces are declared using the <em>namespace</em>
keyword. A file containing a namespace must declare the namespace
at the top of the file before any other code - with one exception: the
<a href="control-structures.declare.html" class="xref">declare</a> keyword.
<div class="example" id="example-234">
<p><strong>Example #1 Declaring a single namespace</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">namespace </span><span style="color: #0000BB">MyProject</span><span style="color: #007700">;<br /><br />const </span><span style="color: #0000BB">CONNECT_OK </span><span style="color: #007700">= </span><span style="color: #0000BB">1</span><span style="color: #007700">;<br />class </span><span style="color: #0000BB">Connection </span><span style="color: #007700">{ </span><span style="color: #FF8000">/* ... */ </span><span style="color: #007700">}<br />function </span><span style="color: #0000BB">connect</span><span style="color: #007700">() { </span><span style="color: #FF8000">/* ... */ </span><span style="color: #007700">}<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
The only code construct allowed before a namespace declaration is the
<em>declare</em> statement, for defining encoding of a source file. In addition,
no non-PHP code may precede a namespace declaration, including extra whitespace:
<div class="example" id="example-235">
<p><strong>Example #2 Declaring a single namespace</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<html><br /><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">namespace </span><span style="color: #0000BB">MyProject</span><span style="color: #007700">; </span><span style="color: #FF8000">// fatal error - namespace must be the first statement in the script<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="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.
</p>
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