When to Use the Array Merge Operator in PHP?

Array Concatenation with the Operator: Unveiled

In PHP, the operator can be utilized to combine two arrays. However, there are instances where this method behaves unexpectedly, as demonstrated by the code snippet below:

<code class="php">$array = array('Item 1');

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

var_dump($array);</code>

This code produces an output of:

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

Contrary to expectations, the second item was not added to the array. To understand this behavior, we delve into the intricacies of array keys.

When using the operator to concatenate arrays, it assigns a key of 0 to all elements. Consequently, any existing elements with different keys are overwritten. To avoid this, the recommended approach is to employ the array_merge() function:

<code class="php">$arr1 = array('foo');
$arr2 = array('bar');

$combined = array_merge($arr1, $arr2);</code>

This code correctly merges the arrays, resulting in:

array('foo', 'bar');

However, if the keys in the arrays are unique, the operator can be employed effectively:

<code class="php">$arr1 = array('one' => 'foo');
$arr2 = array('two' => 'bar');

$combined = $arr1 + $arr2;</code>

This code produces the desired output:

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

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