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>create_function</TITLE
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><H1
><A
NAME="function.create-function"
>create_function</A
></H1
><DIV
CLASS="refnamediv"
><A
NAME="AEN12926"
></A
><P
>    (PHP4 &#62;= 4.0.1)</P
>create_function&nbsp;--&nbsp;Create an anonymous (lambda-style) function</DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN12929"
></A
><H2
>Description</H2
><DIV
CLASS="funcsynopsis"
><A
NAME="AEN12931"
></A
><P
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>string <B
CLASS="function"
>create_function</B
></CODE
> (string args, string code)</CODE
></P
><P
></P
></DIV
><P
>&#13;     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
>&#13;     You can use this function, to (for example) create a function
     from information gathered at run time:
     <TABLE
WIDTH="100%"
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CELLSPACING="0"
CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN12944"
></A
><P
><B
>Example 1. 
       Creating an anonymous function with <B
CLASS="function"
>create_function()</B
>
      </B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;$newfunc = create_function('$a,$b','return "ln($a) + ln($b) = ".log($a * $b);');
echo "New anonymous function: $newfunc\n";
echo $newfunc(2,M_E)."\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
      </PRE
></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
>
     Or, perhaps to have general handler function that can apply a set
     of operations to a list of parameters:
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CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN12948"
></A
><P
><B
>Example 2. 
       Making a general processing function with
       <B
CLASS="function"
>create_function()</B
>
      </B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;function process($var1, $var2, $farr) {
    for ($f=0; $f &#60; count($farr); $f++)
    echo $farr[$f]($var1,$var2)."\n";
}

// create a bunch of math functions
$f1 = 'if ($a &#62;=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 &#62; 0 &#38;&#38; $b != 0) {return "ln(a)/b = ".log($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,&#38;$p)."($p%)";')
    );
echo "\nUsing the second array of anonymous functions\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
      </PRE
></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
>
     and when you run the code above, the output will be:
     <DIV
CLASS="informalexample"
><A
NAME="AEN12952"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;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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><TR
><TD
><DIV
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><A
NAME="AEN12956"
></A
><P
><B
>Example 3. Using anonymous functions as callback functions</B
></P
><TABLE
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><TR
><TD
><PRE
CLASS="programlisting"
>&#13;$av = array("the ","a ","that ","this ");
array_walk($av, create_function('&#38;$v,$k','$v = $v."mango";'));
print_r($av);  // for PHP 3 use var_dump()
// outputs:
// Array
// (
//   [0] =&#62; the mango
//   [1] =&#62; a mango
//   [2] =&#62; that mango
//   [3] =&#62; 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] =&#62; small
//   [1] =&#62; larger
//   [2] =&#62; a big string
//   [3] =&#62; 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] =&#62; it is a string thing
//   [1] =&#62; a big string
//   [2] =&#62; larger
//   [3] =&#62; small
// )
     </PRE
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