How Does PHP's ' ' Operator Differ from `array_merge()` When Combining Arrays?

Merging Arrays with the " " Operator in PHP

When using the " " operator on arrays, PHP performs an array union operation. This operation combines the elements of two arrays into a new array. However, if a key exists in both arrays, the element from the left-hand array is preserved.

In the example provided:

$test = array('hi');
$test += array('test', 'oh');
var_dump($test);

The output is:

array(2) {
  [0] => string(2) "hi"
  [1] => string(2) "oh"
}

This demonstrates that the element "test" from the right-hand array is ignored, and the existing element "hi" is preserved.

Technically, the " " operator performs the following logic:

1. Creates a new array with the elements from the left-hand array.
2. Iterates over the right-hand array and adds any elements that do not already exist in the new array.

This behavior is different from array_merge(). When using array_merge(), the elements from both arrays are combined, with the latter array overwriting any duplicate keys.

Example using array_merge():

print_r(array_merge($test, array('test', 'oh')));

Output:

Array
(
    [0] => hi
    [1] => test // Overwritten from the right-hand array
    [2] => oh
)

Understanding this distinction is important when working with arrays in PHP. The " " operator provides a convenient way to selectively merge array elements, while array_merge() performs a more comprehensive combination.

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