create_function
(PHP 4 >= 4.0.1, PHP 5)
create_function — Create an anonymous (lambda-style) function
说明
string create_function ( string $args , string $code )Creates an anonymous function from the parameters passed, and returns a unique name for it.
参数
Usually these parameters will be passed as single quote delimited strings. 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.
- args
-
The function arguments.
- code
-
The function code.
返回值
Returns a unique function name as a string, or FALSE on error.
范例
Example #1
Creating an anonymous function with create_function()
You can use this function, to (for example) create a function from
information gathered at run time:
<?php
$newfunc = create_function('$a,$b', 'return "ln($a) + ln($b) = " . log($a * $b);');
echo "New anonymous function: $newfunc
";
echo $newfunc(2, M_E) . "
";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?>
Or, perhaps to have general handler function that can apply a set of operations to a list of parameters:
Example #2
Making a general processing function with
create_function()
以上例程会输出：
<?php
function process($var1, $var2, $farr)
{
foreach ($farr as $f) {
echo $f($var1, $var2) . "
";
}
}
// 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 "
Using the first array of anonymous functions
";
echo "parameters: 2.3445, M_PI
";
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 "$b"
** Look the same to me! (looking at the first 3 chars)";'),
create_function('$a,$b', '; return "CRCs: " . crc32($a) . ", ".crc32($b);'),
create_function('$a,$b', '; return "similar(a,b) = " . similar_text($a, $b, &$p) . "($p%)";')
);
echo "
Using the second array of anonymous functions
";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
?>
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, 342550513
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 以上例程会输出：
an array of strings ordered from shorter to longer
以上例程会输出：
sort it from longer to shorter
以上例程会输出：
<?php
$av = array("the ", "a ", "that ", "this ");
array_walk($av, create_function('&$v,$k', '$v = $v . "mango";'));
print_r($av);
?>
Array
(
[0] => the mango
[1] => a mango
[2] => that mango
[3] => this mango
)
<?php
$sv = array("small", "larger", "a big string", "it is a string thing");
print_r($sv);
?>
Array
(
[0] => small
[1] => larger
[2] => a big string
[3] => it is a string thing
)
<?php
usort($sv, create_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);
?>
Array
(
[0] => it is a string thing
[1] => a big string
[2] => larger
[3] => small
)
参见
