In PHP 7.1 we can do the following:
<?php
[$a, $b, $c] = ['a', 'b', 'c'];
?>
Before, we had to do:
<?php
list($a, $b, $c) = ['a', 'b', 'c'];
?>
(PHP 4, PHP 5, PHP 7, PHP 8)
list — Присваивает переменным значения как массиву
Как и конструкция array(), это не функция, а языковая конструкция. Конструкцией list() пользуются, чтобы присваивать списку переменных значения за одну операцию. Строки нельзя распаковать, а выражения list() нельзя вызывать без аргументов.
Замечание:
До PHP 7.1.0 конструкция list() работала только с индексными массивами и принимала числовые индексы начиная с 0.
Начиная с PHP 7.1.0 для деструктуризации массивов с нецелочисленными или непоследовательными ключами в конструкции list() разрешили указывать явные ключи. Подробнее об этом рассказывает блок «Деструктуризация массива».
varПеременная.
varsОстальные переменные.
Функция возвращает массив переменных, которым присвоила значения.
| Версия | Описание |
|---|---|
| 7.3.0 | Добавили поддержку присваивания по ссылкам при деструктуризации массива. |
| 7.1.0 | Теперь в конструкции list() разрешается указывать ключи. Это помогает разыменовывать ассоциативные массивы и массивы с индексами не по порядку. |
Пример #1 Примеры присваивания переменным значений конструкцией list()
<?php
$info = array('кофе', 'коричневый', 'кофеин');
// Перечисляем переменные
list ($drink, $color, $power) = $info;
echo "$drink - $color, а $power делает его особенным.\n";
// Перечисляем только часть переменных
list ($drink,, $power) = $info;
echo "В $drink есть $power.\n";
// Пропускаем все переменные, кроме третьей
list (,, $power) = $info;
echo "Мне нужен $power!\n";
// Конструкция list() не работает со строками
list ($bar) = "abcde";
var_dump($bar); // NULL
?>
Пример #2 Пример присваивания значений переменным конструкцией list()
<?php
$result = $pdo->query("SELECT id, name FROM employees");
while (list ($id, $name) = $result->fetch(PDO::FETCH_NUM)) {
echo "id: $id, name: $name\n";
}
?>
Пример #3 Пример работы вложенной конструкции list()
<?php
list ($a, list ($b, $c)) = array(1, array(2, 3));
var_dump($a, $b, $c);
?>int(1) int(2) int(3)
Пример #4 Пример поведения конструкции list() с определениями порядка индексов
Порядок определения индексов в массиве, который обработает языковая конструкция list(), неважен.
<?php
$foo = array(2 => 'a', 'foo' => 'b', 0 => 'c');
$foo[1] = 'd';
list ($x, $y, $z) = $foo;
var_dump($foo, $x, $y, $z);
?>Следующий параграф показывает вывод, который сформирует пример. Обратите внимание на порядок элементов сравнения в массиве и порядок, в котором элементы записали в синтаксисе конструкции list():
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"
Пример #5 Пример присваивания значений переменным конструкцией list() с указанием ключей
Начиная с PHP 7.1.0 конструкции list() разрешили содержать явные ключи, которые указывают как произвольные выражения. Конструкция принимает смесь строковых и целочисленных ключей; но нельзя смешивать элементы с ключами и без ключей.
<?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, $fourth\n";
?>Результат выполнения приведённого примера:
id: 1, name: Tom id: 2, name: Fred 2, 4
In PHP 7.1 we can do the following:
<?php
[$a, $b, $c] = ['a', 'b', 'c'];
?>
Before, we had to do:
<?php
list($a, $b, $c) = ['a', 'b', 'c'];
?>Since PHP 7.1, keys can be specified
exemple :
<?php
$array = ['locality' => 'Tunis', 'postal_code' => '1110'];
list('postal_code' => $zipCode, 'locality' => $locality) = $array;
print $zipCode; // will output 1110
print $locality; // will output Tunis
?>The example showing that:
$info = array('kawa', 'brązowa', 'kofeina');
list($a[0], $a[1], $a[2]) = $info;
var_dump($a);
outputs:
array(3) {
[2]=>
string(8) "kofeina"
[1]=>
string(5) "brązowa"
[0]=>
string(6) "kawa"
}
One thing to note here is that if you define the array earlier, e.g.:
$a = [0, 0, 0];
the indexes will be kept in the correct order:
array(3) {
[0]=>
string(4) "kawa"
[1]=>
string(8) "brązowa"
[2]=>
string(7) "kofeina"
}
Thought that it was worth mentioning.As noted, list() will give an error if the input array is too short. This can be avoided by array_merge()'ing in some default values. For example:
<?php
$parameter = 'name';
list( $a, $b ) = array_merge( explode( '=', $parameter ), array( true ) );
?>
However, you will have to array_merge with an array long enough to ensure there are enough elements (if $parameter is empty, the code above would still error).
An alternate approach would be to use array_pad on the array to ensure its length (if all the defaults you need to add are the same).
<?php
$parameter = 'bob-12345';
list( $name, $id, $fav_color, $age ) = array_pad( explode( '-', $parameter ), 4, '' );
var_dump($name, $id, $fav_color, $age);
/* outputs
string(3) "bob"
string(5) "12345"
string(0) ""
string(0) ""
*/
?>It can be convenient to specify a default value in case an element is missing in the list. You can use operator + for this:
<?php
$someArray = ['color' => 'orange'];
['color' => $color, 'size' => $size] = $someArray + ['color' => null, 'size' => null];
?>
This will avoid the warning `Undefined array key "size"` you would encounter otherwise.<?php
/**
* It seems you can skip listed values.
* Here's an example to show what I mean.
*
* FYI works just as well with PHP 7.1 shorthand list syntax.
* Tested against PHP 5.6.30, 7.1.5
*/
$a = [ 1, 2, 3, 4 ];
// this is quite normal use case for list
echo "Unpack all values\n";
list($v1, $v2, $v3, $v4) = $a;
echo "$v1, $v2, $v3, $v4\n";
unset($v1, $v2, $v3, $v4);
// this is what I mean:
echo "Skip middle\n";
list($v1, , , $v4) = $a;
echo "$v1, $v2, $v3, $v4\n";
unset($v1, $v2, $v3, $v4);
echo "Skip beginning\n";
list( , , $v3, $v4) = $a;
echo "$v1, $v2, $v3, $v4\n";
unset($v1, $v2, $v3, $v4);
echo "Skip end\n";
list($v1, $v2, , ) = $a;
echo "$v1, $v2, $v3, $v4\n";
unset($v1, $v2, $v3, $v4);
echo "Leave middle\n";
list( , $v2, $v3, ) = $a;
echo "$v1, $v2, $v3, $v4\n";
unset($v1, $v2, $v3, $v4);The example states the following:
<?php
// list() doesn't work with strings
list($bar) = "abcde";
var_dump($bar);
// output: NULL
?>
If the string is in a variable however, it seems using list() will treat the string as an array:
<?php
$string = "abcde";
list($foo) = $string;
var_dump($foo);
// output: string(1) "a"
?>Don't miss simple array pattern matching since php 7
<?php
[$a] = ['hello!'];
var_dump($a); // 'hello!'
$arr = [4 => 50];
[4 => $fifty] = $arr;
var_dump($fifty); // 50
$multidimensionalArray = [['id' => 15, 'email' => 'diyor024@gmail.com']];
[['id' => $id, 'email' => $email]] = $multidimensionalArray;
var_dump($id, $email); // 15 diyor024@gmail.com
?>list() can be used with foreach
<?php
$array = [[1, 2], [3, 4], [5, 6]];
foreach($array as list($odd, $even)){
echo "$odd is odd; $even is even", PHP_EOL;
}
?>
The output:
===
1 is odd; 2 is even
3 is odd; 4 is even
5 is odd; 6 is evenThe list construct seems to look for a sequential list of indexes rather taking elements in sequence. What that obscure statement means is that if you unset an element, list will not simply jump to the next element and assign that to the variable but will treat the missing element as a null or empty variable:
$test = array("a","b","c","d");
unset($test[1]);
list($a,$b,$c)=$test;
print "\$a='$a' \$b='$b' \$c='$c'<BR>";
results in:
$a='a' $b='' $c='c'
not:
$a='a' $b='c' $c='d'Setting it like <?php list($var1,$varN) = null ?> does _not_ raise an E_NOTICE (or other error) and afaics effectively equals an https://php.net/function.unset of $var1,$varN.
I note this as contrasting with the fact that PHP triggers an E_NOTICE about "Undefined offset" "if there aren't enough array elements to fill the list()", as attow documented for https://php.net/control-structures.foreach#control-structures.foreach.list and here only noted in https://php.net/function.list#122951 by Mardaneus.
For completeness, a bash(1) (v5.0 or 4.3 on macos10.13) cli test producing the same result for all my PHP-versions (installed via macports.org) follows. It's also tested with php7.3 using bash5.0 on Debian10:
bash --noprofile --norc -c 'for php in php{{53..56},{70..73}};do for literal in "array()" null;do echo -n $php …=$literal:&&$php -n -d error_reporting=E_ALL -r "var_dump(list(\$var)=$literal);";done;done'
# Above produces the same result pairs per version from:
php53 …=array():
Notice: Undefined offset: 0 in Command line code on line 1
array(0) {
}
# ... to:
php73 …=null:NULLThe list() definition won't throw an error if your array is longer then defined list.
<?php
list($a, $b, $c) = array("a", "b", "c", "d");
var_dump($a); // a
var_dump($b); // b
var_dump($c); // c
?>For PHP 7.1 on, the documentation states that integer and string keys can be mixed, but that elements with and without keys cannot. Here is an example, using data from getimagesize() with mixed keys:
<?php
$data=[
0=> 160,
1 => 120,
2 => 2,
3 => 'width="160" height="120"',
'mime' => 'image/jpeg'
];
list(0=>$width,1=>$height,2=>$type,3=>$dimensions,'mime'=>$mime)=$data;
?>
Here, the numeric keys also need to be specified, as if the whole array is treated as an associative array.
As noted elsewhere, the list() operator can be written in array format:
<?php
[0=>$width,1=>$height,2=>$type,3=>$dimensions,'mime'=>$mime]=$data;
?>This is something I haven't seen in documentation.
Since PHP 7.1, you can use short-hand list unpacking using square brackets, just like short-hand array declaration:
<?php
$foo = ['a', 'b', 'c'];
// short-hand array definition
[$a, $b, $c] = $foo;
echo $a; // displays "a"
// it's same like:
list($x, $y, $z) = $foo;
echo $x; // displays "a"
?>list($a, $b, $c) = ["blue", "money", 32];
shortcut:
[$a, $b, $c] = ["blue", "money", 32];From PHP Version 7.1 you can specify keys in list(), or its new shorthand [] syntax. This enables destructuring of arrays with non-integer or non-sequential keys.
<?php
$data = [
["id" => 1, "name" => 'Tom'],
["id" => 2, "name" => 'Fred'],
];
// list() style
list("id" => $id1, "name" => $name1) = $data[0];
// [] style
["id" => $id1, "name" => $name1] = $data[0];
// list() style
foreach ($data as list("id" => $id, "name" => $name)) {
// logic here with $id and $name
}
// [] style
foreach ($data as ["id" => $id, "name" => $name]) {
// logic here with $id and $name
}Since 7.1.0, you can use an array directly without list():
<?php
[$test, $test2] = explode(",", "hello, world");
echo $test . $test2; // hello, world
?>a simple example of use to swap two variables :
$a = 'hello';
$b = 'world';
list($a, $b) = [$b, $a];
echo $a . ' ' . $b; //display "world hello"
another example :
function getPosition($x, $y, $z)
{
// ... some operations like $x++...
return [$x, $y, $z];
}
list($x, $y, $z) = getPosition($x ,$y, $z);Since PHP 7.1 the [] may now be used as an alternative to the existing list() syntax:
<?php
[$number, $message] = explode('|', '123|Hello World!');
?>If you want use the undefined behaviour as you might expect it e.g. if you want:
$b = ['a','b']; list($a, $b) = $b;
to result in $a=='a' and $b=='b', then you can just cast $b to an array (even although it already is) to create a copy. e.g.
$b = ['a','b']; list($a, $b) = (array)$b;
and get the expected results.Unless you specify keys when using list() it expects the array being fed into it to start at 0.
So having the following code will result in a notice level warning "Undefined offset: 0" and variables not filling as expected
<?php
list($c1, $c2, $c3) = array [1 =>'a', 2 => 'b', 3 => 'c'];
var_dump($c1); // NULL
var_dump($c2); // string(1) "a"
var_dump($c3); // string(1) "b"
?>UNDOCUMENTED BEHAVIOR:
list($a,$b,$c) = null;
in fact works like:
$a = null; $b = null; $c = null;
...So correspondingly:
list($rows[]) = null;
Will increment count($rows), just as if you had executed $rows[] = null;
Watch out for this (for example) when retrieving entire tables from a database, e.g.
while (list($rows[]) = $mysqlresult->fetch_row());
This will leave an extra 'null' entry as the last element of $rows.Easy way to get actual date and time values in variables.
list($day,$month,$year,$hour,$minute,$second) = explode('-',date('d-m-Y-G-i-s'));
echo "$day-$month-$year $hour".":".$minute.":".$second;As of PHP 7.3, lists now support array destructuring - see here: https://www.php.net/manual/en/migration73.new-features.php