create_function
(PHP 4 >= 4.0.1)
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:
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 $newfunc(2, M_E) . "\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?>
Or, perhaps to have general handler function that can apply
a set of operations to a list of parameters:
Example 2. Making a general processing function with create_function()
<?php
function process($var1, $var2, $farr)
{
for ($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()
