What does array + do in PHP?
In PHP it's possible to do array + array. The "plus" sign is a shorthand way of merging arrays, but there's a difference in how they are merged compared to using
Let's imagine these two arrays:
$first = [ 'a', 'b', ]; $second = [ 'c', ];
Merging them using
+ would result in the following:
$first + $second; // ['a', 'b']
array_merge, would result in this:
array_merge($first, $second); // ['a', 'b', 'c']
What's happening here is that
array_merge will override existing keys, while
+ will not. In other words: when a key exists in the first array,
+ will not merge an item with the same key from another array into the first one.
In our example, both arrays actually had numerical keys, like so:
$first = [ 0 => 'a', 1 => 'b', ]; $second = [ 0 => 'c', ];
Which explains why
$first + $second doesn't add 'c' as an element: there already is an item with index
0 in the original.
The same applies for textual keys:
$first = [ 'a' => 'a', 'b' => 'b', ]; $second = [ 'a' => 'a - override', ]; $first + $second; // ['a' => 'a', 'b' => 'b']
+ also works with nested arrays:
$first = [ 'level 1' => [ 'level 2' => 'original' ], ]; $second = [ 'level 1' => [ 'level 2' => 'override' ], ];
+ will keep the
original value, while
One more thing to mention is that
+ will apply the same behaviour when merging multidimensional arrays.