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# create_function

(PHP 4 >= 4.0.1, PHP 5)

create_function -- Create an anonymous (lambda-style) function

## Description

string create_function ( string args, string code)

Creates an anonymous function from the parameters passed, and returns a unique name for it. Usually the `args` will be passed as a single quote delimited string, and this is also recommended for the `code`. The reason for using single quoted strings, is to protect the variable names from parsing, otherwise, if you use double quotes there will be a need to escape the variable names, e.g. `\$avar`.

You can use this function, to (for example) create a function from information gathered at run time:

예 1. Creating an anonymous function with create_function()

`<?php $newfunc = create_function('$a,$b', 'return "ln($a) + ln($b) = " . log($a * $b);'); echo "New anonymous function: $newfunc\n"; echo $newfunc(2, M_E) . "\n"; // outputs // New anonymous function: lambda_1 // ln(2) + ln(2.718281828459) = 1.6931471805599 ?>`

Or, perhaps to have general handler function that can apply a set of operations to a list of parameters:

예 2. Making a general processing function with create_function()

`<?php
function process($var1, $var2, $farr)
{
for ($f=0; $f < count($farr); $f++) {
echo $farr[$f]($var1, $var2) . "\n";
}
}
// create a bunch of math functions
$f1 = 'if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;}';
$f2 = "return \"min(b^2+a, a^2,b) = \".min(\$a*\$a+\$b,\$b*\$b+\$a);";
$f3 = 'if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; }';
$farr = array(
create_function('$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', $f1),
create_function('$a,$b', $f2),
create_function('$a,$b', $f3)
);
echo "\nUsing the first array of anonymous 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 anonymous functions\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
?>`

and when you run the code above, the output will be:

    Using the first array of anonymous 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 anonymous functions
    ** "Twas the night" and "Twas brilling and the slithy toves"
    ** Look the same to me! (looking at the first 3 chars)
    CRCs: -725381282 , 1908338681
    similar(a,b) = 11(45.833333333333%)

But perhaps the most common use for of lambda-style (anonymous) functions is to create callback functions, for example when using array_walk() or usort()

예 3. Using anonymous functions as callback functions

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

outputs:

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

an array of strings ordered from shorter to longer

`<?php $sv = array("small", "larger", "a big string", "it is a string thing"); print_r($sv); ?>`

outputs:

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

sort it from longer to shorter

`<?php usort($sv, create_function('$a,$b','return strlen($b) - strlen($a);')); print_r($sv); ?>`

outputs:

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

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