<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.create-function" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>create_function</refname>
  <refpurpose>Create a function dynamically by evaluating a string of code</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
  &warn.deprecated.function-7-2-0.removed-8-0-0;
 </refsynopsisdiv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>string</type><methodname>create_function</methodname>
   <methodparam><type>string</type><parameter>args</parameter></methodparam>
   <methodparam><type>string</type><parameter>code</parameter></methodparam>
  </methodsynopsis>
  <para>
   Creates a function dynamically from the parameters passed, and returns a unique name for it.
  </para>
  <caution>
   <para>
    This function internally performs an <function>eval</function> and as such has the
    same security issues as <function>eval</function>. It also has bad performance
    and memory usage characteristics, because the created functions are global and
    can not be freed.
   </para>
   <para>
    A native
    <link linkend="functions.anonymous">anonymous function</link> should be used instead.
   </para>
  </caution>
 </refsect1>
 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   It is normally advisable to pass these parameters as
   <link linkend="language.types.string.syntax.single">single quoted</link>
   strings. If using <link linkend="language.types.string.syntax.double">double quoted</link>
   strings, variable names in the code need to be escaped carefully, e.g.
   <literal>\$somevar</literal>.
   <variablelist>
    <varlistentry>
     <term><parameter>args</parameter></term>
     <listitem>
      <para>
       The function arguments, as a single comma-separated string.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>code</parameter></term>
     <listitem>
      <para>
       The function code.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns a unique function name as a string, &return.falseforfailure;.
   Note that the name contains a non-printable character (<literal>"\0"</literal>),
   so care should be taken when printing the name or incorporating it in any other
   string.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>
     Creating a function dynamically, with <function>create_function</function>
     or anonymous functions
    </title>
    <para>
     You can use a dynamically created function, to (for example) create a function from
     information gathered at run time. First, using <function>create_function</function>:
    </para>
    <programlisting role="php">
<![CDATA[
<?php
$newfunc = create_function('$a,$b', 'return "ln($a) + ln($b) = " . log($a * $b);');
echo $newfunc(2, M_E) . "\n";
?>
]]>
    </programlisting>
    <para>
     Now the same code, using an <link linkend="functions.anonymous">anonymous function</link>;
     note that the code and arguments are no longer contained in strings:
    </para>
    <programlisting role="php">
<![CDATA[
<?php
$newfunc = function($a,$b) { return "ln($a) + ln($b) = " . log($a * $b); };
echo $newfunc(2, M_E) . "\n";
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
ln(2) + ln(2.718281828459) = 1.6931471805599
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title>
     Making a general processing function, with <function>create_function</function>
     or anonymous functions
    </title>
    <para>
     Another use could be to have general handler function that can apply a set
     of operations to a list of parameters:
    </para>
    <programlisting role="php">
<![CDATA[
<?php
function process($var1, $var2, $farr)
{
    foreach ($farr as $f) {
        echo $f($var1, $var2) . "\n";
    }
}

// create a bunch of math functions
$farr = array(
    create_function('$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', 'if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;}'),
    create_function('$a,$b', "return \"min(b^2+a, a^2,b) = \".min(\$a*\$a+\$b,\$b*\$b+\$a);"),
    create_function('$a,$b', 'if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; }')
);

echo "\nUsing the first array of dynamic 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 dynamic functions\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
?>
]]>
    </programlisting>
    <para>
     Again, here is the same code using
     <link linkend="functions.anonymous">anonymous functions</link>.
     Note that variable names in the code no longer need to be escaped,
     because they are not enclosed in a string.
    </para>
    <programlisting role="php">
<![CDATA[
<?php
function process($var1, $var2, $farr)
{
    foreach ($farr as $f) {
        echo $f($var1, $var2) . "\n";
    }
}

// create a bunch of math functions
$farr = array(
    function($x,$y) { return "some trig: ".(sin($x) + $x*cos($y)); },
    function($x,$y) { return "a hypotenuse: ".sqrt($x*$x + $y*$y); },
    function($a,$b) { if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;} },
    function($a,$b) { return "min(b^2+a, a^2,b) = " . min($a*$a+$b, $b*$b+$a); },
    function($a,$b) { if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; } }
);

echo "\nUsing the first array of dynamic functions\n";
echo "parameters: 2.3445, M_PI\n";
process(2.3445, M_PI, $farr);

// now make a bunch of string processing functions
$garr = array(
    function($b,$a) { if (strncmp($a, $b, 3) == 0) return "** \"$a\" " .
        "and \"$b\"\n** Look the same to me! (looking at the first 3 chars)"; },
    function($a,$b) { return "CRCs: " . crc32($a) . ", ".crc32($b); },
    function($a,$b) { return "similar(a,b) = " . similar_text($a, $b, $p) . "($p%)"; }
);
echo "\nUsing the second array of dynamic functions\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
Using the first array of dynamic 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 dynamic functions
** "Twas the night" and "Twas brilling and the slithy toves"
** Look the same to me! (looking at the first 3 chars)
CRCs: 3569586014, 342550513
similar(a,b) = 11(45.833333333333%)
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title>Using dynamic functions as callback functions</title>
    <para>
     Perhaps the most common use for dynamic functions
     is to pass them as callbacks, for example when using
     <function>array_walk</function> or <function>usort</function>.
    </para>
    <programlisting role="php">
<![CDATA[
<?php
$av = array("the ", "a ", "that ", "this ");
array_walk($av, create_function('&$v,$k', '$v = $v . "mango";'));
print_r($av);
?>
]]>
    </programlisting>
    <para>
     Converted to an <link linkend="functions.anonymous">anonymous function</link>:
    </para>
    <programlisting role="php">
<![CDATA[
<?php
$av = array("the ", "a ", "that ", "this ");
array_walk($av, function(&$v,$k) { $v = $v . "mango"; });
print_r($av);
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
Array
(
  [0] => the mango
  [1] => a mango
  [2] => that mango
  [3] => this mango
)
]]>
    </screen>
    <para>
     Sorting strings from longest to shortest with <function>create_function</function>:
    </para>
    <programlisting role="php">
<![CDATA[
<?php
$sv = array("small", "a big string", "larger", "it is a string thing");
echo "Original:\n";
print_r($sv);
echo "Sorted:\n";
usort($sv, create_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);
?>
]]>
    </programlisting>
    <para>
     Converted to an <link linkend="functions.anonymous">anonymous function</link>:
    </para>
    <programlisting role="php">
<![CDATA[
<?php
$sv = array("small", "a big string", "larger", "it is a string thing");
echo "Original:\n";
print_r($sv);
echo "Sorted:\n";
usort($sv, function($a,$b) { return strlen($b) - strlen($a); });
print_r($sv);
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
Original:
Array
(
  [0] => small
  [1] => a big string
  [2] => larger
  [3] => it is a string thing
)
Sorted:
Array
(
  [0] => it is a string thing
  [1] => a big string
  [2] => larger
  [3] => small
)
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><link linkend="functions.anonymous">Anonymous functions</link></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>

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