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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.array-find-key" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>array_find_key</refname>
<refpurpose>Returns the key of the first element satisfying a callback function</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>mixed</type><methodname>array_find_key</methodname>
<methodparam><type>array</type><parameter>array</parameter></methodparam>
<methodparam><type>callable</type><parameter>callback</parameter></methodparam>
</methodsynopsis>
<simpara>
<function>array_find_key</function> returns the key of the first element of an
&array; for which the given <parameter>callback</parameter> returns &true;.
If no matching element is found the function returns &null;.
</simpara>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<variablelist>
<varlistentry>
<term><parameter>array</parameter></term>
<listitem>
<simpara>
The &array; that should be searched.
</simpara>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>callback</parameter></term>
<listitem>
<para>
The callback function to call to check each element, which must be
<methodsynopsis>
<type>bool</type><methodname><replaceable>callback</replaceable></methodname>
<methodparam><type>mixed</type><parameter>value</parameter></methodparam>
<methodparam><type>mixed</type><parameter>key</parameter></methodparam>
</methodsynopsis>
If this function returns &true;, the key is returned from
<function>array_find_key</function> and the callback will not be called
for further elements.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<simpara>
The function returns the key of the first element for which the
<parameter>callback</parameter> returns &true;. If no matching element is
found the function returns &null;.
</simpara>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<example>
<title><function>array_find_key</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
$array = [
'a' => 'dog',
'b' => 'cat',
'c' => 'cow',
'd' => 'duck',
'e' => 'goose',
'f' => 'elephant'
];
// Find the first animal with a name longer than 4 characters.
var_dump(array_find_key($array, function (string $value) {
return strlen($value) > 4;
}));
// Find the first animal whose name begins with f.
var_dump(array_find_key($array, function (string $value) {
return str_starts_with($value, 'f');
}));
// Find the first animal where the array key is the first symbol of the animal.
var_dump(array_find_key($array, function (string $value, $key) {
return $value[0] === $key;
}));
// Find the first animal where the array key matching a RegEx.
var_dump(array_find_key($array, function ($value, $key) {
return preg_match('/^([a-f])$/', $key);
}));
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
string(1) "e"
NULL
string(1) "c"
string(1) "a"
]]>
</screen>
</example>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<simplelist>
<member><function>array_find</function></member>
<member><function>array_all</function></member>
<member><function>array_any</function></member>
<member><function>array_filter</function></member>
<member><function>array_reduce</function></member>
</simplelist>
</refsect1>
</refentry>
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