The spread operator support for argument unpacking first existed in PHP 5.6, and this RFC expands on the usage to arrays; both arrays and objects that support Traversable can be expanded. Here’s a basic example from the RFC:

$parts = ['apple', 'pear'];
$fruits = ['banana', 'orange', ...$parts, 'watermelon'];
// ['banana', 'orange', 'apple', 'pear', 'watermelon'];

And even more examples below:

$arr1 = [1, 2, 3];
$arr2 = [...$arr1]; // [1, 2, 3]
$arr3 = [0, ...$arr1]; // [0, 1, 2, 3]
$arr4 = array(...$arr1, ...$arr2, 111); // [1, 2, 3, 1, 2, 3, 111]
$arr5 = [...$arr1, ...$arr1]; // [1, 2, 3, 1, 2, 3]

function getArr() {
  return ['a', 'b'];
}
$arr6 = [...getArr(), 'c']; // ['a', 'b', 'c']

$arr7 = [...new ArrayIterator(['a', 'b', 'c'])]; // ['a', 'b', 'c']

function arrGen() {
    for($i = 11; $i < 15; $i++) {
        yield $i;
    }
}
$arr8 = [...arrGen()]; // [11, 12, 13, 14]

String keys are not supported; you can only use indexed arrays. The author of the RFC explains key support as follows:

In order to make the behavior consistent with argument unpacking , string keys are not supported. A recoverable error will be thrown once a string key is encountered.

To learn about the full details of this accepted proposal, check out the PHP: rfc:spread_operator_for_array. Much thanks to CHU Zhaowei for writing this RFC (and everyone involved). This will for sure be an excellent addition to PHP!

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