📤 PHP Spread Operator – Function & Array Expansion Guide

🧲 Introduction – Why PHP Spread Operator Matters

The spread operator (...) in PHP is a powerful feature introduced in PHP 5.6 and enhanced in later versions. It provides a concise and elegant way to unpack arrays or arguments into functions or merge arrays — reducing boilerplate code.

🎯 In this guide, you’ll learn:

• What the spread operator is and how it works
• How to use it in function arguments and arrays
• Version-specific behaviors
• Practical examples and limitations

📘 What is the Spread Operator in PHP?

The spread operator ... is used to expand arrays or traversables into individual elements. It’s most commonly used for:

• Unpacking arguments into a function call
• Unpacking arrays into a new array (PHP 7.4+)

🧪 Syntax & Use Cases

✅ 1. Spread in Function Arguments (PHP 5.6+)

function sum($a, $b, $c) {
  return $a + $b + $c;
}

$values = [1, 2, 3];
echo sum(...$values);  // Output: 6

📘 Explanation:
The spread operator unpacks the array elements and passes them as individual arguments to the function.

✅ 2. Spread in Function Definitions (Variadic Parameters – PHP 5.6+)

function greet(...$names) {
  foreach ($names as $name) {
    echo "Hello, $name\n";
  }
}

greet("Alice", "Bob", "Charlie");

📘 Explanation:
Here, ...$names collects any number of arguments into an array.

✅ 3. Spread in Array Expressions (PHP 7.4+)

$arr1 = [1, 2];
$arr2 = [3, 4];

$merged = [...$arr1, ...$arr2];
print_r($merged);

🔍 Output:

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
)

📘 Explanation:
You can use ... to unpack arrays directly inside another array. Keys are reindexed unless associative.

✅ 4. Spread with Associative Arrays (PHP 8.1+)

$a = ["x" => 1];
$b = ["y" => 2];
$combined = ["z" => 0, ...$a, ...$b];
print_r($combined);

🔍 Output:

Array
(
    [z] => 0
    [x] => 1
    [y] => 2
)

📘 Explanation:
From PHP 8.1 onward, associative arrays are preserved when using spread syntax.

⚠️ Version Compatibility

❗ Limitations

• ❌ Cannot spread null or non-array values
• ❌ Associative keys are only preserved in PHP 8.1+
• ❌ Cannot unpack strings or scalar types

📌 Summary – Recap & Next Steps

The PHP spread operator helps you write shorter, cleaner, and more readable code, especially when working with dynamic arrays and function arguments.

🔍 Key Takeaways:

• ... unpacks arrays into arguments or array items
• Use in function calls (...$array) or variadic functions (function fn(...$args))
• Spread in array context requires PHP 7.4+ (associative arrays in PHP 8.1+)

⚙️ Real-World Relevance:
Used in argument forwarding, dynamic merging, variadic utilities, and API request building.

❓ Frequently Asked Questions (FAQs)

❓ What is the spread operator in PHP?
✅ It expands arrays or arguments using the ... syntax.

❓ Can I use the spread operator to merge arrays?
✅ Yes. Use [...$array1, ...$array2] (requires PHP 7.4+).

❓ Does it preserve keys in associative arrays?
✅ Only in PHP 8.1 and above.

❓ What’s the difference between ...$array in call vs definition?
✅ In a function call, it unpacks; in a function definition, it collects arguments.