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create_function (PHP 4 >= 4.0.1, PHP 5) create_function -- Create an anonymous (lambda-style) function Descriptionstring 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:
Example 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 $newfunc(2, M_E) . "\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?>
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Or, perhaps to have general handler function that can apply a set
of operations to a list of parameters:
Example 2.
Making a general processing function with
create_function()
<?php
function process($var1, $var2, $farr)
{
foreach ($farr as $f) {
echo $f($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);
?>
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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%) |
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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()
Example 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);
?>
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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);
?>
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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);
?>
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outputs:
Array
(
[0] => it is a string thing
[1] => a big string
[2] => larger
[3] => small
) |
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