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>create_function</H1
><DIV
CLASS="refnamediv"
><A
NAME="AEN29218"
></A
><P
> (PHP 4 >= 4.0.1)</P
>create_function -- Create an anonymous (lambda-style) function</DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN29221"
></A
><H2
>Description</H2
>string <B
CLASS="methodname"
>create_function</B
> ( string args, string code)<BR
></BR
><P
> Creates an anonymous function from the parameters passed, and
returns a unique name for it. Usually the
<TT
CLASS="parameter"
><I
>args</I
></TT
> will be passed as a single quote
delimited string, and this is also recommended for the
<TT
CLASS="parameter"
><I
>code</I
></TT
>. 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.
<TT
CLASS="literal"
>\$avar</TT
>.
</P
><P
> You can use this function, to (for example) create a function
from information gathered at run time:
<TABLE
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CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN29237"
></A
><P
><B
>Example 1.
Creating an anonymous function with <B
CLASS="function"
>create_function()</B
>
</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>$newfunc = create_function('$a,$b','return "ln($a) + ln($b) = ".log($a * $b);');
echo "New anonymous function: $newfunc\n";
echo $newfunc(2,M_E)."\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599</PRE
></TD
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>
Or, perhaps to have general handler function that can apply a set
of operations to a list of parameters:
<TABLE
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><TD
><DIV
CLASS="example"
><A
NAME="AEN29241"
></A
><P
><B
>Example 2.
Making a general processing function with
<B
CLASS="function"
>create_function()</B
>
</B
></P
><TABLE
BORDER="0"
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><TR
><TD
><PRE
CLASS="php"
>function process($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", $garr);</PRE
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>
and when you run the code above, the output will be:
<DIV
CLASS="informalexample"
><A
NAME="AEN29245"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
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><TR
><TD
><PRE
CLASS="programlisting"
>Using the first array of anonymous functions
parameters: 2.3445, M_PI
some trig: -1.6291725057799
a hypotenuse: 3.9199852871011
b*a^2 = 4.8103313314525
min(b^2+a, a^2,b) = 8.6382729035898
ln(a/b) = 0.27122299212594
Using the second array of anonymous functions
** "Twas the night" and "Twas brilling and the slithy toves"
** Look the same to me! (looking at the first 3 chars)
CRCs: -725381282 , 1908338681
similar(a,b) = 11(45.833333333333%)</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
But perhaps the most common use for of lambda-style (anonymous) functions
is to create callback functions, for example when using
<A
HREF="function.array-walk.html"
><B
CLASS="function"
>array_walk()</B
></A
> or <A
HREF="function.usort.html"
><B
CLASS="function"
>usort()</B
></A
>
<TABLE
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><DIV
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><A
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></A
><P
><B
>Example 3. Using anonymous functions as callback functions</B
></P
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><PRE
CLASS="php"
>$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
// )</PRE
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