《PHP》『雜項函式庫』create_function --- 建立匿名函式
create_function
(PHP4 >= 4.0.1)
create_function --- 建立匿名函式
語法 : string create_function (string args, string code)
說明 :
從傳遞的參數建立一個匿名的函式，並且傳回一個獨一無二的名稱。通常參數args將會傳遞成一個單引號字串，而參數code也是如此，使用單引號字串的理由是為了要從剖析中來保護變數名稱，否則，如果你使用雙引號的話，就必須要逃脫變數名稱，例如 : \$avar。
你可以使用這個函式，從執行時收集到的資訊來建立一個函式。
Example :
<?php
$newfunc = create_function('$a,$b','return "ln($a) + ln($b) = ".log($a * $b);');
echo "New anonymous function: $newfunc\n";
echo $newfunc(2,M_E)."\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?>
或者是擁有處理者(handler)函式，這可以請求一個運作的設定到一個參數的列表。
Example :
<?php
function process($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);
?>
當你執行上面的範例時，輸出將會是 :
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%)
匿名函式常見的使用是用來建立callback函式，例如 : 當使用array_walk( )或usort( )時 :
<?php
$av = array("the ","a ","that ","this ");
array_walk($av, create_function('&$v,$k','$v = $v."mango";'));
print_r($av); // for PHP3 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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本帖最後由 蔡逸竹 於 2006-9-24 12:42 編輯 ]
