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PHP - Spread Operator

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.

Example 1

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);
?>

It will produce the following output −

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

Example 2

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);
?>

It will produce the following output −

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

Example 3

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);
?>

It will produce the same output −

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.

Example 4

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);
?>

It will produce the following output −

x = 10  y = 20  z = 30

Example 5

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);
?>

It will produce the following output −

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