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https://github.com/sigmasternchen/php-doc-en
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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@345209 c90b9560-bf6c-de11-be94-00142212c4b1
358 lines
8.1 KiB
XML
358 lines
8.1 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<refentry xml:id="function.list" xmlns="http://docbook.org/ns/docbook">
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<refnamediv>
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<refname>list</refname>
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<refpurpose>Assign variables as if they were an array</refpurpose>
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</refnamediv>
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<refsect1 role="description">
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&reftitle.description;
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<methodsynopsis>
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<type>array</type><methodname>list</methodname>
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<methodparam><type>mixed</type><parameter>var1</parameter></methodparam>
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<methodparam rep="repeat" choice="opt"><type>mixed</type><parameter>...</parameter></methodparam>
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</methodsynopsis>
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<para>
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Like <function>array</function>, this is not really a function,
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but a language construct. <function>list</function> is used to
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assign a list of variables in one operation.
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</para>
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<note>
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<para>
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Before PHP 7.1.0, <function>list</function> only worked on numerical arrays and assumes
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the numerical indices start at 0.
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</para>
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</note>
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<warning>
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<para>
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In PHP 5, <function>list</function> assigns the values starting with the
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right-most parameter. In PHP 7, <function>list</function> starts with the
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left-most parameter.
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</para>
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<para>
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If you are using plain variables, you don't have to worry about this. But
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if you are using arrays with indices you usually expect the order of the
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indices in the array the same you wrote in the <function>list</function>
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from left to right, which is not the case in PHP 5, as it's assigned in the
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reverse order.
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</para>
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<para>
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Generally speaking, it is advisable to avoid relying on a specific order
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of operation, as this may change again in the future.
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</para>
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</warning>
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<warning>
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<para>
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Modification of the array during <function>list</function> execution (e.g.
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using <literal>list($a, $b) = $b</literal>) results in undefined behavior.
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</para>
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</warning>
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</refsect1>
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<refsect1 role="parameters">
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&reftitle.parameters;
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>var1</parameter></term>
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<listitem>
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<para>
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A variable.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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Returns the assigned array.
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</para>
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</refsect1>
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<refsect1 role="changelog">
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&reftitle.changelog;
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<para>
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<informaltable>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>&Version;</entry>
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<entry>&Description;</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>7.1.0</entry>
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<entry>
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It is now possible to specify keys in <function>list</function>. This
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enables destructuring of arrays with non-integer or non-sequential keys.
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</entry>
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</row>
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<row>
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<entry>7.0.0</entry>
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<entry>
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<link linkend="migration70.incompatible.variable-handling.list.order">
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The order that the assignment operations are performed in has
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changed.
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</link>
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</entry>
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</row>
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<row>
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<entry>7.0.0</entry>
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<entry>
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<link linkend="migration70.incompatible.variable-handling.list.empty">
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<function>list</function> expressions can no longer be completely
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empty.
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</link>
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</entry>
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</row>
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<row>
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<entry>7.0.0</entry>
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<entry>
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<link linkend="migration70.incompatible.variable-handling.list.string">
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Strings can no longer be unpacked.
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</link>
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</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</para>
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</refsect1>
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<refsect1 role="examples">
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&reftitle.examples;
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<para>
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<example>
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<title><function>list</function> examples</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$info = array('coffee', 'brown', 'caffeine');
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// Listing all the variables
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list($drink, $color, $power) = $info;
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echo "$drink is $color and $power makes it special.\n";
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// Listing some of them
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list($drink, , $power) = $info;
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echo "$drink has $power.\n";
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// Or let's skip to only the third one
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list( , , $power) = $info;
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echo "I need $power!\n";
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// list() doesn't work with strings
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list($bar) = "abcde";
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var_dump($bar); // NULL
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<para>
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<example>
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<title>An example use of <function>list</function></title>
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<programlisting role="php">
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<![CDATA[
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<table>
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<tr>
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<th>Employee name</th>
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<th>Salary</th>
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</tr>
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<?php
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$result = $pdo->query("SELECT id, name, salary FROM employees");
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while (list($id, $name, $salary) = $result->fetch(PDO::FETCH_NUM)) {
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echo " <tr>\n" .
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" <td><a href=\"info.php?id=$id\">$name</a></td>\n" .
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" <td>$salary</td>\n" .
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" </tr>\n";
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}
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?>
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</table>
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]]>
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</programlisting>
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</example>
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</para>
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<para>
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<example>
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<title>Using nested <function>list</function></title>
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<programlisting role="php">
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<![CDATA[
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<?php
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list($a, list($b, $c)) = array(1, array(2, 3));
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var_dump($a, $b, $c);
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?>
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]]>
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</programlisting>
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<screen>
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<![CDATA[
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int(1)
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int(2)
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int(3)
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]]>
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</screen>
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</example>
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</para>
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<para>
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<example>
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<title>Using <function>list</function> with array indices</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$info = array('coffee', 'brown', 'caffeine');
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list($a[0], $a[1], $a[2]) = $info;
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var_dump($a);
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?>
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]]>
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</programlisting>
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<para>
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Gives the following output (note the order of the elements compared in
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which order they were written in the <function>list</function> syntax):
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</para>
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&example.outputs.7;
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<screen>
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<![CDATA[
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array(3) {
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[0]=>
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string(6) "coffee"
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[1]=>
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string(5) "brown"
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[2]=>
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string(8) "caffeine"
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}
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]]>
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</screen>
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&example.outputs.5;
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<screen>
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<![CDATA[
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array(3) {
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[2]=>
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string(8) "caffeine"
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[1]=>
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string(5) "brown"
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[0]=>
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string(6) "coffee"
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}
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]]>
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</screen>
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</example>
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</para>
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<para>
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<example>
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<title><function>list</function> and order of index definitions</title>
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<simpara>
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The order in which the indices of the array to be consumed by
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<function>list</function> are defined is irrelevant.
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</simpara>
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<programlisting role="php">
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<![CDATA[
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<?php
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$foo = array(2 => 'a', 'foo' => 'b', 0 => 'c');
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$foo[1] = 'd';
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list($x, $y, $z) = $foo;
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var_dump($foo, $x, $y, $z);
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]]>
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</programlisting>
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<para>
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Gives the following output (note the order of the elements compared in
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which order they were written in the <function>list</function> syntax):
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</para>
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<screen>
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<![CDATA[
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array(4) {
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[2]=>
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string(1) "a"
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["foo"]=>
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string(1) "b"
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[0]=>
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string(1) "c"
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[1]=>
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string(1) "d"
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}
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string(1) "c"
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string(1) "d"
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string(1) "a"
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]]>
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</screen>
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</example>
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</para>
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<para>
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<example>
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<title><function>list</function> with keys</title>
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<simpara>
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As of PHP 7.1.0 <function>list</function> can now also contain
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explicit keys, which can be given as arbitrary expressions.
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Mixing of integer and string keys is allowed; however, elements
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with and without keys cannot be mixed.
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</simpara>
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<programlisting role="php">
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<![CDATA[
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<?php
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$data = [
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["id" => 1, "name" => 'Tom'],
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["id" => 2, "name" => 'Fred'],
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];
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foreach ($data as ["id" => $id, "name" => $name]) {
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echo "id: $id, name: $name\n";
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}
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echo PHP_EOL;
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list(1 => $second, 3 => $fourth) = [1, 2, 3, 4];
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echo "$second, $fourth\n";
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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id: 1, name: Tom
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id: 2, name: Fred
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2, 4
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]]>
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</screen>
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</example>
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</para>
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</refsect1>
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<refsect1 role="seealso">
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&reftitle.seealso;
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<para>
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<simplelist>
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<member><function>each</function></member>
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<member><function>array</function></member>
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<member><function>extract</function></member>
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</simplelist>
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</para>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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