Anonymous functions allow creation of functions without specifying their name. They are most useful in callback parameters but the usage is not limited to that.
Example #1 Anonymous function example
<?php
echo preg_replace_callback('~-([a-z])~', function ($match) {
return strtoupper($match[1]);
}, 'hello-world');
// outputs helloWorld
?>
Anonymous functions are internally implemented by the Closure class.
Note: Anonymous functions are available since PHP 5.3.0.