A few operators work on whole arrays.
| Operator | Name | Result |
|---|---|---|
$a + $b | Union | Items of $a, plus items of $b whose keys are missing from $a |
$a == $b | Equality | Same key/value pairs |
$a === $b | Identity | Same pairs, same order, same types |
$a != $b or $a <> $b | Inequality | Not equal |
$a !== $b | Non-identity | Not identical |
Union: +
index.php
PHP
<?php
$defaults = ["theme" => "light", "lang" => "en"];
$custom = ["theme" => "dark"];
$settings = $custom + $defaults;
print_r($settings);
Output
OUTPUT
Array
(
[theme] => dark
[lang] => en
)Keys from the left array win. $defaults only fills in what $custom lacks. That makes + a neat way to apply defaults.
The numeric key trap
For indexed arrays the keys are 0, 1, 2. Union keeps the left items at those keys and ignores the right items with the same keys.
index.php
PHP
<?php
$a = ["a", "b"];
$b = ["x", "y", "z"];
print_r($a + $b);
Output
OUTPUT
Array
(
[0] => a
[1] => b
[2] => z
)If you want to join two lists, use array_merge() or the spread operator instead. See Common Array Functions.
index.php
PHP
<?php
print_r(array_merge(["a", "b"], ["x", "y", "z"]));
Output
OUTPUT
Array
(
[0] => a
[1] => b
[2] => x
[3] => y
[4] => z
)Equality and identity
index.php
PHP
<?php
$one = ["a" => 1, "b" => 2];
$two = ["b" => 2, "a" => 1];
$three = ["a" => "1", "b" => 2];
var_dump($one == $two); // same pairs, order ignored
var_dump($one === $two); // order differs
var_dump($one == $three); // 1 == "1"
var_dump($one === $three); // types differ
Output
OUTPUT
bool(true)
bool(false)
bool(true)
bool(false)
lightbulb
Pick by intent
Want “defaults for missing keys”? Use
+. Want “put these lists together”? Use array_merge() or [...$a, ...$b].