PHP Spread Operator (...): Unpack and Merge Arrays

The spread operator ... unpacks an array into separate items. You can use it in function calls and inside array literals.

Merge arrays

index.php

PHP

<?php
$frontend = ["html", "css"];
$backend = ["php", "sql"];

$skills = [...$frontend, ...$backend, "git"];

echo implode(", ", $skills);

Output

OUTPUT

html, css, php, sql, git

Spread into function arguments

index.php

PHP

<?php
function area(int $width, int $height): int
{
    return $width * $height;
}

$size = [4, 5];

echo area(...$size);

Output

OUTPUT

String keys (PHP 8.1+)

Since PHP 8.1, you can spread arrays that have string keys. Later keys replace earlier ones.

index.php

PHP

<?php
$defaults = ["theme" => "light", "lang" => "en"];
$custom = ["theme" => "dark"];

$settings = [...$defaults, ...$custom];

print_r($settings);

Output

OUTPUT

Array
(
    [theme] => dark
    [lang] => en
)

This is how you apply “defaults, then overrides”. The right-hand array wins.

Spread vs + vs array_merge()

Expression	Result for key `"theme"`	Numeric keys
`$a + $b`	The left value wins	Left items kept, right ones with the same index ignored
`array_merge($a, $b)`	The right value wins	Re-numbered
`[...$a, ...$b]`	The right value wins	Re-numbered

index.php

PHP

<?php
$a = ["x" => 1, 5 => "five"];
$b = ["x" => 2, 5 => "cinco"];

print_r($a + $b);
print_r([...$a, ...$b]);

Output

OUTPUT

Array
(
    [x] => 1
    [5] => five
)
Array
(
    [x] => 2
    [0] => five
    [1] => cinco
)

Copy and add

The spread operator is a tidy way to make a modified copy without changing the original.

index.php

PHP

<?php
$cart = ["pen", "book"];

$newCart = [...$cart, "bag"];

echo count($cart) . " vs " . count($newCart);

Output

OUTPUT

2 vs 3

Spread works on anything traversable

You can spread a generator or another Traversable too, not only arrays.

index.php

PHP

<?php
function numbers(): Generator
{
    yield 1;
    yield 2;
}

print_r([...numbers(), 3]);

Output

OUTPUT

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
)

info

Variadics use the same dots

In a function definition, ...$args collects arguments. In a call or array, ...$array spreads them out. Same symbol, opposite directions. See Variadic Functions.