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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:

示範 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:

示範 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()

示範 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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