Spread Operator (...)

Also Known As

TL;DR

Explanation

PHP's spread operator (...) serves two purposes: in function signatures it collects remaining arguments into an array (variadic), and in call sites or array literals it unpacks an iterable into individual elements. Since PHP 8.1, string-keyed arrays can be spread in function calls (named arguments). This enables array merging ($merged = [...$a, ...$b]) as a readable alternative to array_merge(), and passing stored argument lists to functions.

Common Misconception

Why It Matters

Common Mistakes

• Spreading a non-array or non-Traversable — causes a TypeError at runtime.
• Using spread for array merging when array_merge() semantics (re-indexing numerics, last-write-wins for strings) are needed.
• Spreading associative arrays in PHP 7 — string key spread was only added in PHP 8.1.
• Not knowing spread works in array literals: $merged = [...$defaults, ...$overrides].

Code Examples

// Old verbose approach:
$args = [1, 2, 3];
call_user_func_array('array_merge', $arrays); // Replaced by spread

// With spread operator:
function sum(int ...$nums): int { return array_sum($nums); }
$numbers = [1, 2, 3];
echo sum(...$numbers); // Clean argument unpacking

// Spread in function calls
function add(int $a, int $b, int $c): int { return $a + $b + $c; }
$args = [1, 2, 3];
echo add(...$args); // 6

// Spread in array literals
$first  = [1, 2, 3];
$second = [4, 5, 6];
$merged = [...$first, ...$second]; // [1,2,3,4,5,6]

// PHP 8.1 — spread with string keys (named arguments style)
$defaults = ['color' => 'blue', 'size' => 'M'];
$options  = ['size' => 'XL', ...$defaults]; // ['size' => 'M', 'color' => 'blue']
// Note: later keys win — order matters

// Variadic parameters
function sum(int ...$nums): int { return array_sum($nums); }
sum(1, 2, 3); // 6

References

• ↗ https://www.php.net/manual/en/functions.arguments.php#functions.variable-arg-list

Tags

Related Terms