Starting with the version 5.3, PHP introduced Anonymous functions, known as Closures.
This type of functions have no specified name. They are most useful as the value of callback.

1. Example, Anonymous function as callback function.
<?php
$arr = array(' hello word ', ' Have <b>good day</b>');

// removes tags and whitespace from the beginning and end of each array element
// capitalize the first character of each word
$arr = array_map(function($elm){
 return ucwords(trim(strip_tags($elm)));
}, $arr);

var_export($arr);            // array ( 0 => 'Hello Word', 1 => 'Have Good Day' )
?>

2. Closures can also be used as the values of variables (notice how the function is called, using the variable name, including the $ character).
<?php
$website = function($name) {
  return 'http://www.'. $name. '.net';
};

echo $website('coursesweb');           // https://coursesweb.net
echo $website('marplo');               // https://marplo.net
?>

3. Closures can also be used inside another function. In the following example it is used closures to create HTML List elements.
<?php
// receives an array with elements that will form the <li>
function ulList($ar_items) {
  $li = function($item) {
    return '<li>'. $item. '</li>';
  };

  // traverse the array received in parameter, calls $li() to create the <ul><li>
  $ul = '<ul>';
  foreach($ar_items as $item) {
    $ul .= $li($item);
  }
  $ul .= '<ul>';

  return $ul;
}

$ar_items = array('li 1', 'li 2', 'li 3');
echo ulList($ar_items);         // <ul><li>li 1</li><li>li 2</li><li>li 3</li><ul>
?>

- Another example with anonymous function inside other function. Notice the using of the use() , to can use the outside variables inside anonymous function.
<?php
function test($a) {
  $b = $a / 2;
  $c = function($a) use($b) {
    return $a + $b;
  };

  return $c($a);
}

echo test(10);         // 15
?>

4. Closures can be a useful tool for object-oriented programming. Starting with PHP 5.4 , $this can be used in anonymous functions.
<?php
class A {
  private $value = 1;
  public function getVal() {
    return function() { return $this->value * 2; };
  }
}

$a = new A;
echo $a->getVal();        // 2
?>

Daily Test with Code Example

HTML
CSS
JavaScript
PHP-MySQL
Which tag is used in <table> to create table header cell?
<thead> <th> <td>
<table><tr>
  <th>Title 1</th>
  <th>Title 2</th>
</tr></table>
Which CSS property sets the distance between lines?
line-height word-spacing margin
.some_class {
  line-height: 150%;
}
Which function opens a new browser window.
alert() confirm() open()
document.getElementById("id_button").onclick = function(){
  window.open("http://coursesweb.net/");
}
Indicate the PHP function that returns an array with names of the files and folders inside a directory.
mkdir() scandir() readdir()
$ar_dir = scandir("dir_name");
var_export($ar_dir);
PHP Anonymous functions - Closures

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