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');           // http://coursesweb.net
echo $website('marplo');               // http://www.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 type of <input> creates input fields that should contain a numeric value?
type="text" type="number" type="date"
<input type="number" name="points" min="5" max="80" />
Which CSS property allows to change the transparency of an element?
font-style opacity color
#id {
  filter:alpha(opacity=40);    /* for IE */
  opacity:0.4;
}
Click on the function that formats a number to specified number of characters.
toPrecision() exp() toFixed()
var num = 12.34567;
alert( num.toPrecision(3) );       // 12.3
Which function randomizes the order of the elements into an array?
natsort() shuffle() sort()
$lang = array(10=>"PHP", 20=>"JavaScript", "site"=>"coursesweb.net");
shuffle($lang);
var_export($lang);     // array (0=>"coursesweb.net", 1=>"PHP", 2=>"JavaScript")
PHP Anonymous functions - Closures

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