php-doc-en/reference/array/functions/list.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.list" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>list</refname>
  <refpurpose>Assign variables as if they were an array</refpurpose>
 </refnamediv>
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>array</type><methodname>list</methodname>
   <methodparam><type>mixed</type><parameter>var</parameter></methodparam>
   <methodparam rep="repeat" choice="opt"><type>mixed</type><parameter>vars</parameter></methodparam>
  </methodsynopsis>
  <para>
   Like <function>array</function>, this is not really a function,
   but a language construct. <function>list</function> is used to
   assign a list of variables in one operation.
   Strings can not be unpacked and <function>list</function> expressions 
   can not be completely empty.
  </para>
  <note>
   <para>
    Before PHP 7.1.0, <function>list</function> only worked on numerical arrays and assumes
    the numerical indices start at 0.
   </para>
  </note>
 </refsect1>
 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>var</parameter></term>
     <listitem>
      <para>
       A variable.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
   <variablelist>
    <varlistentry>
     <term><parameter>vars</parameter></term>
     <listitem>
      <para>
       Further variables.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>
 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the assigned array.
  </para>
 </refsect1>
 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>7.3.0</entry>
       <entry>
        Support for reference assignments in array destructuring was added.
       </entry>
      </row>
      <row>
       <entry>7.1.0</entry>
       <entry>
        It is now possible to specify keys in <function>list</function>. This
        enables destructuring of arrays with non-integer or non-sequential keys.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>
 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>list</function> examples</title>
    <programlisting role="php">
<![CDATA[
<?php

$info = array('coffee', 'brown', 'caffeine');

// Listing all the variables
list($drink, $color, $power) = $info;
echo "$drink is $color and $power makes it special.\n";

// Listing some of them
list($drink, , $power) = $info;
echo "$drink has $power.\n";

// Or let's skip to only the third one
list( , , $power) = $info;
echo "I need $power!\n";

// list() doesn't work with strings
list($bar) = "abcde";
var_dump($bar); // NULL
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title>An example use of <function>list</function></title>
    <programlisting role="php">
<![CDATA[
<?php
$result = $pdo->query("SELECT id, name FROM employees");
while (list($id, $name) = $result->fetch(PDO::FETCH_NUM)) {
    echo "id: $id, name: $name\n";
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title>Using nested <function>list</function></title>
    <programlisting role="php">
<![CDATA[
<?php

list($a, list($b, $c)) = array(1, array(2, 3));

var_dump($a, $b, $c);

?>
]]>
    </programlisting>
    <screen>
<![CDATA[
int(1)
int(2)
int(3)
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title><function>list</function> and order of index definitions</title>
    <simpara>
     The order in which the indices of the array to be consumed by
     <function>list</function> are defined is irrelevant.
    </simpara>
    <programlisting role="php">
<![CDATA[
<?php
$foo = array(2 => 'a', 'foo' => 'b', 0 => 'c');
$foo[1] = 'd';
list($x, $y, $z) = $foo;
var_dump($foo, $x, $y, $z);
]]>
    </programlisting>
    <para>
     Gives the following output (note the order of the elements compared in
     which order they were written in the <function>list</function> syntax):
    </para>
    <screen>
<![CDATA[
array(4) {
  [2]=>
  string(1) "a"
  ["foo"]=>
  string(1) "b"
  [0]=>
  string(1) "c"
  [1]=>
  string(1) "d"
}
string(1) "c"
string(1) "d"
string(1) "a"
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title><function>list</function> with keys</title>
    <simpara>
     As of PHP 7.1.0 <function>list</function> can now also contain
     explicit keys, which can be given as arbitrary expressions.
     Mixing of integer and string keys is allowed; however, elements
     with and without keys cannot be mixed.
    </simpara>
    <programlisting role="php">
<![CDATA[
<?php
$data = [
    ["id" => 1, "name" => 'Tom'],
    ["id" => 2, "name" => 'Fred'],
];
foreach ($data as ["id" => $id, "name" => $name]) {
    echo "id: $id, name: $name\n";
}
echo PHP_EOL;
list(1 => $second, 3 => $fourth) = [1, 2, 3, 4];
echo "$second, $fourth\n";
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
id: 1, name: Tom
id: 2, name: Fred

2, 4
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>each</function></member>
    <member><function>array</function></member>
    <member><function>extract</function></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>

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