create_function

Popis

string create_function ( string args, string code)

Z p°edan²ch argument∙ vytvo°φ anonymnφ funkci, a vrßtφ unikßtnφ nßzev tΘto funkce. args se obvykle p°edßvß jako string v jednoduch²ch uvozovkßch, a doporuΦujeme to i pro code. D∙vodem pro jednoduchΘ uvozovky je ochrana nßzv∙ prom∞nn²ch p°ed parsovßnφm, pokud pou╛ijete dvojitΘ uvozovky, budete muset oescapovat nßzvy prom∞nn²ch, nap°. \$avar.

Tuto funkci m∙╛ete (nap°φklad) pou╛φt k vytvo°enφ funkce z dat shromß╛d∞n²ch za b∞hu programu:
P°φklad 1. Vytvo°enφ anonymnφ funkce pomocφ create_function()
$newfunc = create_function('$a,$b','return "ln($a) + ln($b) = ".log($a * $b);'); echo "New anonymous function: $newfunc\n"; echo $newfunc(2,M_E)."\n"; // v²stup // New anonymous function: lambda_1 // ln(2) + ln(2.718281828459) = 1.6931471805599
Nebo t°eba k vytvo°enφ obecnΘho handleru, kter² na p°edanΘ argumenty aplikuje sadu operacφ:
P°φklad 2. Vytvo°enφ obecnΘ zpracujφcφ funkce pomocφ create_function()
function process($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);
kdy╛ spustφte v²╣euveden² k≤d, v²stup bude:

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%)

Ale z°ejm∞ nejb∞╛n∞j╣φm vyu╛itφm lambda-style (anonymnφch) funkcφ je tvorba callback funkcφ, nap°. pro pou╛itφ v array_walk() nebo usort()

P°φklad 3. Vyu╛itφ anonymnφch funkcφ jako callback funkcφ

$av = array("the ","a ","that ","this ");
array_walk($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
// )