PHP - Spread Operator

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PHP recognizes the three dots symbol (...) as the spread operator. The spread operator is also sometimes called the splat operator. This operator was first introduced in PHP version 7.4. It can be effectively used in many cases such as unpacking arrays.

The spread operator increases the readability of arrays and function parameters. It is a simple but useful feature for modern PHP development.

So here is the list concepts with example, we will cover in this chapter −

• Syntax of PHP Spread Operator

• Expanding an Array with Spread Operator

• Using Spread Operator Multiple Times

• Spread Operator vs array_merge()

• Named Arguments with Spread Operator

• Using Spread Operator with Function Return Value

Syntax

Below is the syntax of the PHP spread operator −

// Expanding an array
$newArray = [...$existingArray];

// Using in a function
function myFunction(...$args) {
   // Function body
}

Expanding an Array with Spread Operator

In the example below, the elements in $arr1 are inserted in $arr2 after a list of its own elements.

<?php
   $arr1 = [4,5];
   $arr2 = [1,2,3, ...$arr1];

   print_r($arr2);
?>

Output

This will produce the following result −

Array
(
   [0] => 1
   [1] => 2
   [2] => 3
   [3] => 4
   [4] => 5
)

Using Spread Operator Multiple Times

The Spread operator can be used more than once in an expression. For example, in the following code, a third array is created by expanding the elements of two arrays.

<?php
   $arr1 = [1,2,3];
   $arr2 = [4,5,6];
   $arr3 = [...$arr1, ...$arr2];

   print_r($arr3);
?>

Output

This will generate the below result −

Array
(
   [0] => 1
   [1] => 2
   [2] => 3
   [3] => 4
   [4] => 5
   [5] => 6
)

Spread Operator vs array_merge()

Note that the same result can be obtained with the use of array_merge() function, as shown below −

<?php
   $arr1 = [1,2,3];
   $arr2 = [4,5,6];
   $arr3 = array_merge($arr1, $arr2);

   print_r($arr3);
?>

Output

This will create the below outcome −

Array
(
   [0] => 1
   [1] => 2
   [2] => 3
   [3] => 4
   [4] => 5
   [5] => 6
)

However, the use of (...) operator is much more efficient as it avoids the overhead a function call.

Named Arguments with Spread Operator

PHP 8.1.0 also introduced another feature that allows using named arguments after unpacking the arguments. Instead of providing a value to each of the arguments individually, the values from an array will be unpacked into the corresponding arguments, using ... (three dots) before the array.

<?php  
   function  myfunction($x, $y, $z=30) {
      echo "x = $x  y = $y  z = $z";
   }

   myfunction(...[10, 20], z:30);
?>

Output

This will lead to the following outcome −

x = 10  y = 20  z = 30

Using Spread Operator with Function Return Value

In the following example, the return value of a function is an array. The array elements are then spread and unpacked.

<?php
   function get_squares() {
      for ($i = 0; $i < 5; $i++) {
         $arr[] = $i**2;
      }
      return $arr;
   }
   $squares = [...get_squares()];
   print_r($squares);
?>

Output

The result of this PHP code is −

Array
(
   [0] => 0
   [1] => 1
   [2] => 4
   [3] => 9
   [4] => 16
)