SunshinePHP 2019

list

(PHP 4, PHP 5, PHP 7)

listAssign variables as if they were an array

Description

array list ( mixed $var1 [, mixed $... ] )

Like array(), this is not really a function, but a language construct. list() is used to assign a list of variables in one operation.

Note:

Before PHP 7.1.0, list() only worked on numerical arrays and assumes the numerical indices start at 0.

Warning

In PHP 5, list() assigns the values starting with the right-most parameter. In PHP 7, list() starts with the left-most parameter.

If you are using plain variables, you don't have to worry about this. But if you are using arrays with indices you usually expect the order of the indices in the array the same you wrote in the list() from left to right, which is not the case in PHP 5, as it's assigned in the reverse order.

Generally speaking, it is advisable to avoid relying on a specific order of operation, as this may change again in the future.

Warning

Modification of the array during list() execution (e.g. using list($a, $b) = $b) results in undefined behavior.

Parameters

var1

A variable.

Return Values

Returns the assigned array.

Changelog

Version Description
7.1.0 It is now possible to specify keys in list(). This enables destructuring of arrays with non-integer or non-sequential keys.
7.0.0 The order that the assignment operations are performed in has changed.
7.0.0 list() expressions can no longer be completely empty.
7.0.0 Strings can no longer be unpacked.

Examples

Example #1 list() examples

<?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
?>

Example #2 An example use of list()

<table>
 <tr>
  <th>Employee name</th>
  <th>Salary</th>
 </tr>

<?php
$result 
$pdo->query("SELECT id, name, salary FROM employees");
while (list(
$id$name$salary) = $result->fetch(PDO::FETCH_NUM)) {
    echo 
" <tr>\n" .
          
"  <td><a href=\"info.php?id=$id\">$name</a></td>\n" .
          
"  <td>$salary</td>\n" .
          
" </tr>\n";
}

?>

</table>

Example #3 Using nested list()

<?php

list($a, list($b$c)) = array(1, array(23));

var_dump($a$b$c);

?>
int(1)
int(2)
int(3)

Example #4 Using list() with array indices

<?php

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

list(
$a[0], $a[1], $a[2]) = $info;

var_dump($a);

?>

Gives the following output (note the order of the elements compared in which order they were written in the list() syntax):

Output of the above example in PHP 7:

array(3) {
  [0]=>
  string(6) "coffee"
  [1]=>
  string(5) "brown"
  [2]=>
  string(8) "caffeine"
}

Output of the above example in PHP 5:

array(3) {
  [2]=>
  string(8) "caffeine"
  [1]=>
  string(5) "brown"
  [0]=>
  string(6) "coffee"
}

Example #5 list() and order of index definitions

The order in which the indices of the array to be consumed by list() are defined is irrelevant.

<?php
$foo 
= array(=> 'a''foo' => 'b'=> 'c');
$foo[1] = 'd';
list(
$x$y$z) = $foo;
var_dump($foo$x$y$z);

Gives the following output (note the order of the elements compared in which order they were written in the list() syntax):

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"

Example #6 list() with keys

As of PHP 7.1.0 list() 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.

<?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(
=> $second=> $fourth) = [1234];
echo 
"$second$fourth\n";

The above example will output:

id: 1, name: Tom
id: 2, name: Fred

2, 4

See Also

  • each() - Return the current key and value pair from an array and advance the array cursor
  • array() - Create an array
  • extract() - Import variables into the current symbol table from an array

add a note add a note

User Contributed Notes 16 notes

up
70
Rhamnia Mohamed
1 year ago
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
?>
up
67
grzeniufication
4 years ago
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.
up
49
grzeniufication
1 year ago
<?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, $v4);
up
70
chris at chlab dot ch
6 years ago
The example states the following:
<?php
// list() doesn't work with strings
list($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"
?>
up
31
carlosv775 at gmail dot com
1 year ago
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'];
?>
up
54
megan at voices dot com
5 years ago
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) ""
*/
?>
up
46
svennd
5 years ago
The 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
?>
up
27
pemapmodder1970 at gmail dot com
2 years ago
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 even
up
3
Mardaneus
5 months ago
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"

?>
up
15
john at jbwalker dot com
5 years ago
The 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'
up
3
anthony dot ossent at live dot fr
2 years ago
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);
up
4
Colin Guthrie
3 years ago
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.
up
2
blazej
1 year ago
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
}
up
1
contato at tobias dot ws
8 months ago
Since PHP 7.1 the [] may now be used as an alternative to the existing list() syntax:

<?php
[$number, $message] = explode('|', '123|Hello World!');
?>
up
3
Dean
3 years ago
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.
up
0
petru at fuxspam dot xtremeweb dot ro
8 months ago
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"

?>
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