Understanding Array Concatenation in PHP

While attempting to combine two arrays using the ' ' operator, users may encounter unexpected results. Here's why the following code doesn't concatenate the arrays as intended:

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

This code will output an array containing only the first item, 'Item 1'. The ' ' operator in PHP performs element-wise addition, not array concatenation. When adding two arrays, it will replace elements with matching keys.

To concatenate arrays, PHP provides the array_merge() function. This function merges the elements of two arrays into a new array while preserving the keys. For example:

$arr1 = array('foo');
$arr2 = array('bar');

$combined = array_merge($arr1, $arr2);

The $combined array will contain both 'foo' and 'bar'.

If the arrays have elements with different keys, the ' ' operator can be used to combine them. However, it's important to note that it will overwrite elements with matching keys. For instance:

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

$combined = $arr1   $arr2;

The $combined array will contain both 'foo' and 'bar', with keys 'one' and 'two' respectively.