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<title>namespace keyword and __NAMESPACE__ constant</title>
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<h2 class="title">namespace keyword and __NAMESPACE__ constant</h2>
<p class="verinfo">(PHP 5 >= 5.3.0)</p>
<p class="para">
PHP supports two ways of abstractly accessing elements within the current namespace,
the <strong><code>__NAMESPACE__</code></strong> magic constant, and the <em>namespace</em>
keyword.
</p>
<p class="para">
The value of <strong><code>__NAMESPACE__</code></strong> is a string that contains the current
namespace name. In global, un-namespaced code, it contains an empty string.
<div class="example" id="example-244">
<p><strong>Example #1 __NAMESPACE__ example, namespaced code</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 />echo </span><span style="color: #DD0000">'"'</span><span style="color: #007700">, </span><span style="color: #0000BB">__NAMESPACE__</span><span style="color: #007700">, </span><span style="color: #DD0000">'"'</span><span style="color: #007700">; </span><span style="color: #FF8000">// outputs "MyProject"<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<div class="example" id="example-245">
<p><strong>Example #2 __NAMESPACE__ example, global code</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /><br /></span><span style="color: #007700">echo </span><span style="color: #DD0000">'"'</span><span style="color: #007700">, </span><span style="color: #0000BB">__NAMESPACE__</span><span style="color: #007700">, </span><span style="color: #DD0000">'"'</span><span style="color: #007700">; </span><span style="color: #FF8000">// outputs ""<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
The <strong><code>__NAMESPACE__</code></strong> constant is useful for dynamically constructing
names, for instance:
<div class="example" id="example-246">
<p><strong>Example #3 using __NAMESPACE__ for dynamic name construction</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 />function </span><span style="color: #0000BB">get</span><span style="color: #007700">(</span><span style="color: #0000BB">$classname</span><span style="color: #007700">)<br />{<br /> </span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">__NAMESPACE__ </span><span style="color: #007700">. </span><span style="color: #DD0000">'\\' </span><span style="color: #007700">. </span><span style="color: #0000BB">$classname</span><span style="color: #007700">;<br /> return new </span><span style="color: #0000BB">$a</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
The <em>namespace</em> keyword can be used to explicitly request
an element from the current namespace or a sub-namespace. It is the namespace
equivalent of the <em>self</em> operator for classes.
<div class="example" id="example-247">
<p><strong>Example #4 the namespace operator, inside a 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 />use </span><span style="color: #0000BB">blah</span><span style="color: #007700">\</span><span style="color: #0000BB">blah </span><span style="color: #007700">as </span><span style="color: #0000BB">mine</span><span style="color: #007700">; </span><span style="color: #FF8000">// see "Using namespaces: importing/aliasing"<br /><br /></span><span style="color: #0000BB">blah</span><span style="color: #007700">\</span><span style="color: #0000BB">mine</span><span style="color: #007700">(); </span><span style="color: #FF8000">// calls function MyProject\blah\mine()<br /></span><span style="color: #007700">namespace\</span><span style="color: #0000BB">blah</span><span style="color: #007700">\</span><span style="color: #0000BB">mine</span><span style="color: #007700">(); </span><span style="color: #FF8000">// calls function MyProject\blah\mine()<br /><br /></span><span style="color: #007700">namespace\</span><span style="color: #0000BB">func</span><span style="color: #007700">(); </span><span style="color: #FF8000">// calls function MyProject\func()<br /></span><span style="color: #007700">namespace\</span><span style="color: #0000BB">sub</span><span style="color: #007700">\</span><span style="color: #0000BB">func</span><span style="color: #007700">(); </span><span style="color: #FF8000">// calls function MyProject\sub\func()<br /></span><span style="color: #007700">namespace\</span><span style="color: #0000BB">cname</span><span style="color: #007700">::</span><span style="color: #0000BB">method</span><span style="color: #007700">(); </span><span style="color: #FF8000">// calls static method "method" of class MyProject\cname<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= new namespace\</span><span style="color: #0000BB">sub</span><span style="color: #007700">\</span><span style="color: #0000BB">cname</span><span style="color: #007700">(); </span><span style="color: #FF8000">// instantiates object of class MyProject\sub\cname<br /></span><span style="color: #0000BB">$b </span><span style="color: #007700">= namespace\</span><span style="color: #0000BB">CONSTANT</span><span style="color: #007700">; </span><span style="color: #FF8000">// assigns value of constant MyProject\CONSTANT to $b<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<div class="example" id="example-248">
<p><strong>Example #5 the namespace operator, in global code</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /><br /></span><span style="color: #007700">namespace\</span><span style="color: #0000BB">func</span><span style="color: #007700">(); </span><span style="color: #FF8000">// calls function func()<br /></span><span style="color: #007700">namespace\</span><span style="color: #0000BB">sub</span><span style="color: #007700">\</span><span style="color: #0000BB">func</span><span style="color: #007700">(); </span><span style="color: #FF8000">// calls function sub\func()<br /></span><span style="color: #007700">namespace\</span><span style="color: #0000BB">cname</span><span style="color: #007700">::</span><span style="color: #0000BB">method</span><span style="color: #007700">(); </span><span style="color: #FF8000">// calls static method "method" of class cname<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= new namespace\</span><span style="color: #0000BB">sub</span><span style="color: #007700">\</span><span style="color: #0000BB">cname</span><span style="color: #007700">(); </span><span style="color: #FF8000">// instantiates object of class sub\cname<br /></span><span style="color: #0000BB">$b </span><span style="color: #007700">= namespace\</span><span style="color: #0000BB">CONSTANT</span><span style="color: #007700">; </span><span style="color: #FF8000">// assigns value of constant CONSTANT to $b<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
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