Best way to initialize (empty) array in PHP

Question

In certain other languages (AS3 for example), it has been noted that initializing a new array is faster if done like this var foo = [] rather than var foo

Answer 1

In ECMAScript implementations (for instance, ActionScript or JavaScript), Array() is a constructor function and [] is part of the array literal grammar. Both are optimized and executed in completely different ways, with the literal grammar not being dogged by the overhead of calling a function.

PHP, on the other hand, has language constructs that may look like functions but aren't treated as such. Even with PHP 5.4, which supports [] as an alternative, there is no difference in overhead because, as far as the compiler/parser is concerned, they are completely synonymous.

// Before 5.4, you could only write
$array = array(
    "foo" => "bar",
    "bar" => "foo",
);

// As of PHP 5.4, the following is synonymous with the above
$array = [
    "foo" => "bar",
    "bar" => "foo",
];

If you need to support older versions of PHP, use the former syntax. There's also an argument for readability but, being a long-time JS developer, the latter seems rather natural to me.  I actually made the mistake of trying to initialise arrays using [] when I was first learning PHP.

This change to the language was originally proposed and rejected due to a majority vote against by core developers with the following reason:

This patch will not be accepted because slight majority of the core developers voted against. Though if you take a accumulated mean between core developers and userland votes seems to show the opposite it would be irresponsible to submit a patch witch is not supported or maintained in the long run.

However, it appears there was a change of heart leading up to 5.4, perhaps influenced by the implementations of support for popular databases like MongoDB (which use ECMAScript syntax).

Answer 2

In PHP an array is an array; there is no primitive vs. object consideration, so there is no comparable optimization to be had.

Answer 3

What you're doing is 100% correct.

In terms of nice naming it's often done that private/protected properties are preceded with an underscore to make it obvious that they're not public. E.g. private $_arr = array() or public $arr = array()

Answer 4

There is no other way, so this is the best.

Edit: This answer is not valid since PHP 5.4 and higher.

Answer 5

Try this:

    $arr = (array) null;
    var_dump($arr);

    // will print
    // array(0) { }

Answer 6

Prior to PHP 5.4:

$myArray = array();

PHP 5.4 and higher

$myArray = [];