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# create_function

(PHP 4 )

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()
    $newfunc = create_function('$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()
    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()

Example 3. Using anonymous functions as callback functions
    $av = array("the ","a ","that ","this ");
    array_walk($av, create_function('&$v,$k','$v = $v."mango";'));
    print_r($av);  // for PHP 3 use var_dump()
    // outputs:
    // Array
    // (
    //   [0] => 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
    // )

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