How big are PHP arrays (and values) really?

Post by sapphirecat » Fri, Dec 16, 2011, 4:48 PM UTC

ars wrote: post #15

Wilya wrote: post #9

Earlier quoted context omitted.

It's funny. I don't have much experience with php, and I had to actually run your last example to know that it appended the values (instead of recreating the array with a single value each time). Is there an append operator, or something more explicit ? '+=' seems to do something strange..

[] IS the append operator. And += only works right if both sides are arrays. If not the right side will be converted. += is really intended for hashmaps, not integer indexes, for those use [].

Post by rorrr » Fri, Dec 16, 2011, 5:27 PM UTC

wlievens wrote: post #26

rorrr wrote: post #20

Earlier quoted context omitted.

I think they are a little more complex than regular hash maps. 1) They keys can be integers or unicode strings (ordering works differently for these two cases) 2) The keys are not necessarily ordered (see ksort and krsort functions, for example).

They are ordered by insertion. That's different from for instance objects in Javascript.

    $arr = array();
    $arr[0] = 'cat';
    $arr[2] = 'dog';
    $arr[1] = 'fish';

    krsort($arr);

    var_dump($arr);

    array(3) 
    {
        [2]=> string(3) "dog" 
        [1]=> string(4) "fish" 
        [0]=> string(3) "cat" 
    }

Post by dspillett » Fri, Dec 16, 2011, 5:33 PM UTC

cygx wrote: post #46

dspillett wrote: post #39

Earlier quoted context omitted.

It is the same for Javascript: even though you have an Array object that you can instantiate instead of the more generic Object, they are much the same thing under the hood with both arrays and objects being hash maps [you can use the two interchangably to an extent (if you don't need the extra functinos defined by the array prototype) - references object properies in an hash-like manner or array contents the same wa…

It is the same for Javascript: even though you have an Array object that you can instantiate instead of the more generic Object, they are much the same thing under the hood with both arrays and objects being hash maps While this is true if you only consider language semantics, implementions do use actual arrays to store dense properties with integer names, ie arrays are backed by both flat and sparse storage with som…

Post by maratd » Fri, Dec 16, 2011, 6:01 PM UTC

fauigerzigerk wrote: post #33

fhars wrote: post #11

Earlier quoted context omitted.

Since PHP arrays are within a factor of two for the theoretical optimum for a dynamically typed language that unifies arrays and hashes, all these languages (add javascript to the list) should have roughly comparable behaviour unless they do some ugly special casing for hashes where all keys are integers. [edit: see the comment by InfernalH for a measurement that indicates that ruby seems to do this.] You have to loo…

As I see it, doing the ugly special casing for you is exactly what any competent dynamic language implementation should do.

Post by fauigerzigerk » Fri, Dec 16, 2011, 7:31 PM UTC

maratd wrote: post #78

fauigerzigerk wrote: post #33

Earlier quoted context omitted.

As I see it, doing the ugly special casing for you is exactly what any competent dynamic language implementation should do.

Ugly special casing requires code that would detect those special cases. This adds overhead in terms of processing cycles and code. Most arrays, majority of the time, store a tiny amount of information. Less than a dozen entries. Doing that sort of detection is massive overkill and would actually hurt performance. You want to speed things up for the real world. Not artificial benchmarks. How many times in your code a…