Function handling Functions
PHP Manual

create_function

Create a function dynamically by evaluating a string of code

Warning

This function has been DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0. Relying on this function is highly discouraged.

Description

string create_function(string $args, string $code)

Creates a function dynamically from the parameters passed, and returns a unique name for it.

Caution

This function internally performs an eval and as such has the same security issues as eval. It also has bad performance and memory usage characteristics, because the created functions are global and can not be freed.

A native anonymous function should be used instead.

Parameters

It is normally advisable to pass these parameters as single quoted strings. If using double quoted strings, variable names in the code need to be escaped carefully, e.g. \$somevar.

args

The function arguments, as a single comma-separated string.

code

The function code.

Return Values

Returns a unique function name as a string, or false on failure. Note that the name contains a non-printable character ("\0"), so care should be taken when printing the name or incorporating it in any other string.

Examples

Example #1 Creating a function dynamically, with create_function or anonymous functions

You can use a dynamically created function, to (for example) create a function from information gathered at run time. First, using create_function: 

<?php
$newfunc = create_function('$a,$b', 'return "ln($a) + ln($b) = " . log($a * $b);');
echo $newfunc(2, M_E) . "\n";
?>

Now the same code, using an anonymous function; note that the code and arguments are no longer contained in strings: 

<?php
$newfunc = function($a,$b) { return "ln($a) + ln($b) = " . log($a * $b); };
echo $newfunc(2, M_E) . "\n";
?>

The above example will output:

ln(2) + ln(2.718281828459) = 1.6931471805599

Example #2 Making a general processing function, with create_function or anonymous functions

Another use could be to have general handler function that can apply a set of operations to a list of parameters: 

<?php
function process($var1, $var2, $farr)
{
    foreach ($farr as $f) {
        echo $f($var1, $var2) . "\n";
    }
}

// create a bunch of math functions
$farr = array(
    create_function('$x,$y', 'return "some trig: ".(sin($x) + $x*cos($y));'),
    create_function('$x,$y', 'return "a hypotenuse: ".sqrt($x*$x + $y*$y);'),
    create_function('$a,$b', 'if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;}'),
    create_function('$a,$b', "return \"min(b^2+a, a^2,b) = \".min(\$a*\$a+\$b,\$b*\$b+\$a);"),
    create_function('$a,$b', 'if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; }')
);

echo "\nUsing the first array of dynamic functions\n";
echo "parameters: 2.3445, M_PI\n";
process(2.3445, M_PI, $farr);

// now make a bunch of string processing functions
$garr = array(
    create_function('$b,$a', 'if (strncmp($a, $b, 3) == 0) return "** \"$a\" '.
        'and \"$b\"\n** Look the same to me! (looking at the first 3 chars)";'),
    create_function('$a,$b', 'return "CRCs: " . crc32($a) . ", ".crc32($b);'),
    create_function('$a,$b', 'return "similar(a,b) = " . similar_text($a, $b, $p) . "($p%)";')
);
echo "\nUsing the second array of dynamic functions\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
?>

Again, here is the same code using anonymous functions. Note that variable names in the code no longer need to be escaped, because they are not enclosed in a string. 

<?php
function process($var1, $var2, $farr)
{
    foreach ($farr as $f) {
        echo $f($var1, $var2) . "\n";
    }
}

// create a bunch of math functions
$farr = array(
    function($x,$y) { return "some trig: ".(sin($x) + $x*cos($y)); },
    function($x,$y) { return "a hypotenuse: ".sqrt($x*$x + $y*$y); },
    function($a,$b) { if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;} },
    function($a,$b) { return "min(b^2+a, a^2,b) = " . min($a*$a+$b, $b*$b+$a); },
    function($a,$b) { if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; } }
);

echo "\nUsing the first array of dynamic functions\n";
echo "parameters: 2.3445, M_PI\n";
process(2.3445, M_PI, $farr);

// now make a bunch of string processing functions
$garr = array(
    function($b,$a) { if (strncmp($a, $b, 3) == 0) return "** \"$a\" " .
        "and \"$b\"\n** Look the same to me! (looking at the first 3 chars)"; },
    function($a,$b) { return "CRCs: " . crc32($a) . ", ".crc32($b); },
    function($a,$b) { return "similar(a,b) = " . similar_text($a, $b, $p) . "($p%)"; }
);
echo "\nUsing the second array of dynamic functions\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
?>

The above example will output:

Using the first array of dynamic functions
parameters: 2.3445, M_PI
some trig: -1.6291725057799
a hypotenuse: 3.9199852871011
b*a^2 = 4.8103313314525
min(b^2+a, a^2,b) = 8.6382729035898
ln(a)/b = 0.27122299212594

Using the second array of dynamic functions
** "Twas the night" and "Twas brilling and the slithy toves"
** Look the same to me! (looking at the first 3 chars)
CRCs: 3569586014, 342550513
similar(a,b) = 11(45.833333333333%)

Example #3 Using dynamic functions as callback functions

Perhaps the most common use for dynamic functions is to pass them as callbacks, for example when using array_walk or usort. 

<?php
$av = array("the ", "a ", "that ", "this ");
array_walk($av, create_function('&$v,$k', '$v = $v . "mango";'));
print_r($av);
?>

Converted to an anonymous function: 

<?php
$av = array("the ", "a ", "that ", "this ");
array_walk($av, function(&$v,$k) { $v = $v . "mango"; });
print_r($av);
?>

The above example will output:

Array
(
  [0] => the mango
  [1] => a mango
  [2] => that mango
  [3] => this mango
)

Sorting strings from longest to shortest with create_function: 

<?php
$sv = array("small", "a big string", "larger", "it is a string thing");
echo "Original:\n";
print_r($sv);
echo "Sorted:\n";
usort($sv, create_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);
?>

Converted to an anonymous function: 

<?php
$sv = array("small", "a big string", "larger", "it is a string thing");
echo "Original:\n";
print_r($sv);
echo "Sorted:\n";
usort($sv, function($a,$b) { return strlen($b) - strlen($a); });
print_r($sv);
?>

The above example will output:

Original:
Array
(
  [0] => small
  [1] => a big string
  [2] => larger
  [3] => it is a string thing
)
Sorted:
Array
(
  [0] => it is a string thing
  [1] => a big string
  [2] => larger
  [3] => small
)