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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
例 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\n";
echo $newfunc(2, M_E) . "\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?> |
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Or, perhaps to have general handler function that can apply a set
of operations to a list of parameters:
例 2.
Making a general processing function with
create_function()
<?php
function process($var1, $var2, $farr)
{
foreach ($farr as $f) {
echo $f($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);
?> |
上例将输出： 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%) |
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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()
例 3. Using anonymous functions as callback functions <?php
$av = array("the ", "a ", "that ", "this ");
array_walk($av, create_function('&$v,$k', '$v = $v . "mango";'));
print_r($av);
?> |
上例将输出： Array
(
[0] => the mango
[1] => a mango
[2] => that mango
[3] => this mango
) |
an array of strings ordered from shorter to longer
<?php
$sv = array("small", "larger", "a big string", "it is a string thing");
print_r($sv);
?> |
上例将输出： Array
(
[0] => small
[1] => larger
[2] => a big string
[3] => it is a string thing
) |
sort it from longer to shorter
<?php
usort($sv, create_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);
?> |
上例将输出： Array
(
[0] => it is a string thing
[1] => a big string
[2] => larger
[3] => small
) |
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