Why Does the ( ) Operator Fail When Combining PHP Arrays?

Concatenating Arrays in PHP: Why Operator Falters

When attempting to join arrays using the " " operator, one may encounter unexpected results. Consider the following code:

$array = array('Item 1');
$array += array('Item 2');
var_dump($array);

Output:

array(1) {
  [0] => string(6) "Item 1"
}

Why doesn't this work?

Keys and Duplicates

The issue lies in array keys and duplicate values. Both arrays in the given code have keys of "0," causing the duplicate values to overwrite each other. To preserve the original order and prevent duplication, PHP uses the first value for the key "0."

Solution: Array Merging

To concatenate arrays correctly, use array_merge():

$arr1 = array('foo'); // Same as array(0 => 'foo')
$arr2 = array('bar'); // Same as array(0 => 'bar')
$combined = array_merge($arr1, $arr2);

array_merge() merges arrays, preserving key-value pairs.

When to Use Operator

The " " operator is still useful when combining arrays with different keys:

$arr1 = array('one' => 'foo');
$arr2 = array('two' => 'bar');
$combined = $arr1 + $arr2;

This will result in:

array('one' => 'foo', 'two' => 'bar');

In summary, use array_merge() for concatenating arrays to preserve order and avoid key conflicts. Use the " " operator for merging arrays with unique keys.

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