Example
A closure is the PHP equivalent of an anonymous function, eg. a function that does not have a name. Even if that is technically not correct, the behavior of a closure remains the same as a function's, with a few extra features.
A closure is nothing but an object of the Closure class which is created by declaring a function without a name. For example:
<?php
$myClosure = function() {
echo 'Hello world!';
};
$myClosure(); // Shows "Hello world!"
Keep in mind that $myClosure is an instance of Closure so that you are aware of what you can truly do with it (cf. http://fr2.php.net/manual/en/class.closure.php )
The classic case you would need a Closure is when you have to give a callable to a function, for instance usort.
Here is an example where an array is sorted by the number of siblings of each person:
<?php
$data = [
[
'name' => 'John',
'nbrOfSiblings' => 2,
],
[
'name' => 'Stan',
'nbrOfSiblings' => 1,
],
[
'name' => 'Tom',
'nbrOfSiblings' => 3,
]
];
usort($data, function($e1, $e2) {
if ($e1['nbrOfSiblings'] == $e2['nbrOfSiblings']) {
return 0;
}
return $e1['nbrOfSiblings'] < $e2['nbrOfSiblings'] ? -1 : 1;
});
var_dump($data); // Will show Stan first, then John and finally Tom
