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    <p>The manual uses the terms "callback" and "callable" interchangeably, however, "callback" traditionally refers to a string or array value that acts like a <a href="http://en.wikipedia.org/wiki/Function_pointer" rel="noreferrer">function pointer</a>, referencing a function or class method for future invocation. This has allowed some elements of functional programming since PHP 4. The flavors are:</p> <pre><code>$cb1 = 'someGlobalFunction'; $cb2 = ['ClassName', 'someStaticMethod']; $cb3 = [$object, 'somePublicMethod']; // this syntax is callable since PHP 5.2.3 but a string containing it // cannot be called directly $cb2 = 'ClassName::someStaticMethod'; $cb2(); // fatal error // legacy syntax for PHP 4 $cb3 = array(&amp;$object, 'somePublicMethod'); </code></pre> <p>This is a safe way to use callable values in general:</p> <pre><code>if (is_callable($cb2)) { // Autoloading will be invoked to load the class "ClassName" if it's not // yet defined, and PHP will check that the class has a method // "someStaticMethod". Note that is_callable() will NOT verify that the // method can safely be executed in static context. $returnValue = call_user_func($cb2, $arg1, $arg2); } </code></pre> <p>Modern PHP versions allow the first three formats above to be invoked directly as <code>$cb()</code>. <code>call_user_func</code> and <code>call_user_func_array</code> support all the above.</p> <p>See: <a href="http://php.net/manual/en/language.types.callable.php" rel="noreferrer">http://php.net/manual/en/language.types.callable.php</a></p> <p>Notes/Caveats: </p> <ol> <li>If the function/class is namespaced, the string must contain the fully-qualified name. E.g. <code>['Vendor\Package\Foo', 'method']</code></li> <li><code>call_user_func</code> does not support passing non-objects by reference, so you can either use <code>call_user_func_array</code> or, in later PHP versions, save the callback to a var and use the direct syntax: <code>$cb()</code>;</li> <li>Objects with an <a href="http://us2.php.net/manual/en/language.oop5.magic.php#language.oop5.magic.invoke" rel="noreferrer"><code>__invoke()</code></a> method (including anonymous functions) fall under the category "callable" and can be used the same way, but I personally don't associate these with the legacy "callback" term.</li> <li>The legacy <code>create_function()</code> creates a global function and returns its name. It's a wrapper for <code>eval()</code> and anonymous functions should be used instead.</li> </ol>
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    1. POHow do I implement a callback in PHP?
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    1. USSteve Clay
    1. USSteve Clay
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    1. POHow do I implement a callback in PHP?
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    1. COThis is vastly better than OP's accepted self-answer.
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      1. USchaos
    2. COIndeed, using the function is the proper way to do it. While using a variable and then just calling it, as suggested in the accepted answer is cool, it's ugly and won't scale well with code.
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      1. USicco
    3. COChanged accepted answer. Agreed with comments, this is a great answer.
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      1. USNick Stinemates
 

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