foreach loop over an associatve array behavior in PHP

Question

When I perform a foreach loop over an associatve array in php, the order in which it is performed is the order in which it is defined.

For example:

$arr = array("z" => "z", "a" => "a", "b" => "b");

foreach($arr as $key => val)
  print("$key: $val\n");

Outputs:

z: z
a: a
b: b

Whereas

$arr = array("a" => "a", "b" => "b", "z" => "z");

Outputs:

a: a
b: b
z: z

So my question is then: is this behavior defined at a specification level? Can I have reasonable certainty that this behavior will not be changed in future versions of PHP?

Answer 1

From the PHP Manual

An array in PHP is actually an ordered map. A map is a type that associates values to keys. This type is optimized for several different uses; it can be treated as an array, list (vector), hash table (an implementation of a map), dictionary, collection, stack, queue, and probably more.

and

Arrays are ordered. The order can be changed using various sorting functions.

So you can be certain (at least currently) that the order will be maintained. I would be very surprised if this behaviour were to change because it is clearly stated and because of this there will be a huge amount of code that relies on it.

Answer 2

This will never change.

Answer 3

Because arrays are always ordered, and the easiest and fastest way to iterate the array is just going from the first element to the last one (so there is no good reason to change the behavior for foreach()), you can be reasonably sure that this behavior will not change.

Answer 4

Your questions seems like you came from programming in Perl where "arrays" are not guaranteed to be in the order you created them. But in PHP it has always been ordered and will always be, otherwise a lot of code will break.