Question

In PHP an Associative Array keeps its order.

// this will keep its order in PHP
a['kiwis']
a['bananas']
a['potatoes']
a['peaches']

However in Flex it doesn’t with a perfectly valid explanation. I really can’t remember how C treats this problem but I am more leaned to believe it works like php as the Array has it’s space pre-reserved in memory and we can just walk the memory. Am I right?

The real question here is why. Why does C/PHP interpretation of this varies from Flash/Flex and what is the main reason Adobe has made Flash work this way.

Thank you.

Answer 1

For PHP arrays: These beasts are unique constructs and are somehow complicated, an overview is given in a slashdot response from Kendall Hopkins (scroll down to his answer):

Ken: The PHP array is a chained hash table (lookup of O(c) and O(n) on key collisions)
that allows for int and string keys. It uses 2 different hashing algorithms
to fit the two types into the same hash key space. Also each value stored in
the hash is linked to the value stored before it and the value stored after
(linked list). It also has a temporary pointer which is used to hold the
current item so the hash can be iterated.

In C/C++, there is, as has been said, no “associative array” in the core lanuage. It has a map (ordered) in the STL, as will be in the new standard library (hash_map, unordered_map) and there was a gnu_hash_map (unordered) on some implementations (which was very good imho).

Furthermore, the “order” of elements in an “ordered” C/C++ map is usually not the “insertion order” (as in PHP), it’s the “key sort order” or “string hash value sort order“.

To answer your question: your view of equivalence of PHP and C/C++ associative arrays does not hold, in PHP, they made a design decision in order to provide maximum comfort under a single interface (and failed or succeeded, whatever). In C/C++, there are many different implementations (with advantages and tradeoffs) available.

Regards

rbo