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.