create_function
(PHP4 >= 4.0.1)
create_function --- 建立匿名函数
语法 :
string create_function(string args, string code)说明 :
从传递的参数建立一个匿名的函数，并且传回一个独一无二的名称。通常参数args将会传递成一个单引号字符串，而参数code也是如此，使用单引号字符串的理由是为了要从剖析中来保护变量名称，否则，如果你使用双引号的话，就必须要逃脱变量名称，例如 : \$avar。
你可以使用这个函数，从执行时收集到的资讯来建立一个函数。
Example :
<?php
$newfunc = create_function('$a,$b','return "ln($a) + ln($b) = ".log($a * $b);');
echo "New anonymous function: $newfunc\n";
echo $newfunc(2,M_E)."\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?>
或者是拥有处理者(handler)函数，这可以请求一个运作的设定到一个参数的列表。
Example :
<?php
function process($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);
?>
当你执行上面的范例时，输出将会是 :
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%)
匿名函数常见的使用是用来建立callback函数，例如 : 当使用array_walk( )或usort( )时 :
<?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
// )
?>