create_function
Create an anonymous (lambda-style) function
Description
stringcreate_function
stringargs
stringcode
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:
Creating an anonymous function with <function>create_function</function>
]]>
Or, perhaps to have general handler function that can apply a set
of operations to a list of parameters:
Making a general processing function with
<function>create_function</function>
=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:
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
Using anonymous functions as callback functions
the mango
[1] => a mango
[2] => that mango
[3] => this mango
)
*/
// an array of strings ordered from shorter to longer
$sv = array("small","larger","a big string","it is a string thing");
print_r($sv);
/*
outputs:
Array
(
[0] => small
[1] => larger
[2] => a big string
[3] => it is a string thing
)
*/
// sort it from longer to shorter
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
)
*/
?>
]]>