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<h2 class="title">Variable functions</h2>
<p class="para">
PHP supports the concept of variable functions. This means that if
a variable name has parentheses appended to it, PHP will look for
a function with the same name as whatever the variable evaluates
to, and will attempt to execute it. Among other things, this can
be used to implement callbacks, function tables, and so forth.
</p>
<p class="para">
Variable functions won't work with language constructs such
as <span class="function"><a href="function.echo.html" class="function">echo</a></span>, <span class="function"><a href="function.print.html" class="function">print</a></span>,
<span class="function"><a href="function.unset.html" class="function">unset()</a></span>, <span class="function"><a href="function.isset.html" class="function">isset()</a></span>,
<span class="function"><a href="function.empty.html" class="function">empty()</a></span>, <span class="function"><a href="function.include.html" class="function">include</a></span>,
<span class="function"><a href="function.require.html" class="function">require</a></span> and the like. Utilize wrapper functions to make
use of any of these constructs as variable functions.
</p>
<p class="para">
<div class="example" id="example-163">
<p><strong>Example #1 Variable function example</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">function </span><span style="color: #0000BB">foo</span><span style="color: #007700">() {<br /> echo </span><span style="color: #DD0000">"In foo()<br />\n"</span><span style="color: #007700">;<br />}<br /><br />function </span><span style="color: #0000BB">bar</span><span style="color: #007700">(</span><span style="color: #0000BB">$arg </span><span style="color: #007700">= </span><span style="color: #DD0000">''</span><span style="color: #007700">)<br />{<br /> echo </span><span style="color: #DD0000">"In bar(); argument was '</span><span style="color: #0000BB">$arg</span><span style="color: #DD0000">'.<br />\n"</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #FF8000">// This is a wrapper function around echo<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">echoit</span><span style="color: #007700">(</span><span style="color: #0000BB">$string</span><span style="color: #007700">)<br />{<br /> echo </span><span style="color: #0000BB">$string</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">$func </span><span style="color: #007700">= </span><span style="color: #DD0000">'foo'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$func</span><span style="color: #007700">(); </span><span style="color: #FF8000">// This calls foo()<br /><br /></span><span style="color: #0000BB">$func </span><span style="color: #007700">= </span><span style="color: #DD0000">'bar'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$func</span><span style="color: #007700">(</span><span style="color: #DD0000">'test'</span><span style="color: #007700">); </span><span style="color: #FF8000">// This calls bar()<br /><br /></span><span style="color: #0000BB">$func </span><span style="color: #007700">= </span><span style="color: #DD0000">'echoit'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$func</span><span style="color: #007700">(</span><span style="color: #DD0000">'test'</span><span style="color: #007700">); </span><span style="color: #FF8000">// This calls echoit()<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
Object methods can also be called with the variable functions syntax.
<div class="example" id="example-164">
<p><strong>Example #2 Variable method example</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">class </span><span style="color: #0000BB">Foo<br /></span><span style="color: #007700">{<br /> function </span><span style="color: #0000BB">Variable</span><span style="color: #007700">()<br /> {<br /> </span><span style="color: #0000BB">$name </span><span style="color: #007700">= </span><span style="color: #DD0000">'Bar'</span><span style="color: #007700">;<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">$name</span><span style="color: #007700">(); </span><span style="color: #FF8000">// This calls the Bar() method<br /> </span><span style="color: #007700">}<br /> <br /> function </span><span style="color: #0000BB">Bar</span><span style="color: #007700">()<br /> {<br /> echo </span><span style="color: #DD0000">"This is Bar"</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #0000BB">$foo </span><span style="color: #007700">= new </span><span style="color: #0000BB">Foo</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$funcname </span><span style="color: #007700">= </span><span style="color: #DD0000">"Variable"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$foo</span><span style="color: #007700">-></span><span style="color: #0000BB">$funcname</span><span style="color: #007700">(); </span><span style="color: #FF8000">// This calls $foo->Variable()<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
When calling static methods, the function call is stronger than the static property operator:
<div class="example" id="example-165">
<p><strong>Example #3 Variable method example with static properties</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">Foo<br /></span><span style="color: #007700">{<br /> static </span><span style="color: #0000BB">$variable </span><span style="color: #007700">= </span><span style="color: #DD0000">'static property'</span><span style="color: #007700">;<br /> static function </span><span style="color: #0000BB">Variable</span><span style="color: #007700">()<br /> {<br /> echo </span><span style="color: #DD0000">'Method Variable called'</span><span style="color: #007700">;<br /> }<br />}<br /><br />echo </span><span style="color: #0000BB">Foo</span><span style="color: #007700">::</span><span style="color: #0000BB">$variable</span><span style="color: #007700">; </span><span style="color: #FF8000">// This prints 'static property'. It does need a $variable in this scope.<br /></span><span style="color: #0000BB">$variable </span><span style="color: #007700">= </span><span style="color: #DD0000">"Variable"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">Foo</span><span style="color: #007700">::</span><span style="color: #0000BB">$variable</span><span style="color: #007700">(); </span><span style="color: #FF8000">// This calls $foo->Variable() reading $variable in this scope.<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
See also <span class="function"><a href="function.is-callable.html" class="function">is_callable()</a></span>, <span class="function"><a href="function.call-user-func.html" class="function">call_user_func()</a></span>,
<a href="language.variables.variable.html" class="link">
variable variables</a> and <span class="function"><a href="function.function-exists.html" class="function">function_exists()</a></span>.
</p>
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