When to use array_merge and union operator (+) in PHP?

array_merge

Use array_merge when you want to merge indexed arrays without keys:

	<?php
	$fruits = array('apples', 'oranges');
	$more_fruits = array('bananas', 'mangoes');
	$all_fruits = array_merge($fruits, $more_fruits);
	print_r($all_fruits);
	?>

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Output:

	Array
	(
	[0] => apples
	[1] => oranges
	[2] => bananas
	[3] => mangoes
	)

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Array Union Operator (+)

Use the union operator when you want to extend an array or override certain key values. A good use case for this is overriding/extending a default settings array with a user defined array (similar to how you would use $.extend while writing a jQuery plugin):

	<?php
	$default_settings = array('page'=>3, 'per_page'=>100);
	$user_override = array('per_page'=>50, 'format'=>'json');
	$overriden_setting = $user_override + $default_settings;
	print_r($overriden_setting);
	?>

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Output:

	Array
	(
	[per_page] => 50
	[format] => json
	[page] => 3
	)

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References

• PHP join two arrays with array_merge and the union operator
• PHP array_merge vs plus union Operator
• + operator for array in PHP?