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Array destructuring in PHP
Array destructuring in PHP
# List or []
In PHP, list
or []
is a so called "language construct", just like array()
.
This language construct is used to "pull" variables out of an array.
In other words: it will "destructure" the array into separate variables.
Note that the word is "destructure", not "destruction" — that's something different 😉
Here's what that looks like:
$array = [1, 2, 3]; // Using the list syntax: list($a, $b, $c) = $array; // Or the shorthand syntax: [$a, $b, $c] = $array; // $a = 1 // $b = 2 // $c = 3
Whether you prefer list
or its shorthand []
is up to you.
People might argue that []
is ambiguous with the shorthand array syntax,
and therefor prefer list
.
I'll be using the shorthand version in code samples though.
So what more can list
do?
# Skip elements
Say you only need the third element of an array, the first two can be skipped by simply not providing a variable.
[, , $c] = $array; // $c = 3
Also note that list
will always start at index 0.
Take for example the following array:
$array = [ 1 => 'a', 2 => 'b', 3 => 'c', ];
The first variable pulled out with list
would be null
,
because there's no element with index 0
.
This might seem like a shortcoming, but luckily there are more possibilities.
# Non-numerical keys
PHP 7.1 allows list
to be used with arrays that have non-numerical keys.
This opens a world of possibilities.
$array = [ 'a' => 1, 'b' => 2, 'c' => 3, ];
['c' => $c, 'a' => $a] = $array;
As you can see, you can change the order however you want, and also skip elements entirely.
# In practice
One of the uses of list
are functions like parse_url
and pathinfo
.
Because these functions return an array with named parameters,
we can use list
to pull out the information we'd like:
[ 'basename' => $file, 'dirname' => $directory, ] = pathinfo('/users/test/file.png');
As you can see, the variables don't need the same name as the key. Also note that destructuring an array with an unknown key will trigger a notice:
[ 'path' => $path, 'query' => $query, ] = parse_url('https://stitcher.io/blog'); // PHP Notice: Undefined index: query
In this case, $query
would be null
.
One last detail: trailing commas are allowed with named destructs, just like you're used to with arrays.
# In loops
You can also use the list construct in loops:
$array = [ [ 'name' => 'a', 'id' => 1 ], [ 'name' => 'b', 'id' => 2 ], ]; foreach ($array as ['id' => $id, 'name' => $name]) { // … }
This could be useful when parsing for example a JSON or CSV file. Be careful though that undefined keys will still trigger a notice.
In summary, there are some pretty good cases in which list
can be of help!