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Date: Sat, 3 Jun 2017 07:34:40 -0700
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Subject: Re: [PHP-DEV] Why hashtable keeps insertion order by default ?
From: thruska@cubiclesoft.com (Thomas Hruska)

On 6/3/2017 1:31 AM, Pawel Por wrote:
> Hi,
> 
> AFAIK the hashtable in PHP by default keeps the order in which the
> elements are inserted. Could you please write me why it keeps the
> insertion order by default ?
> 
> Thanks in advance for clarification.

Because it is a brilliant, high performance solution to extremely 
annoying classical data structures (aka unordered hashes) found in other 
programming and scripting languages.  It's the only sane option to 
present to any language's users and the cost is minimal.  PHP nailed it 
very early on and the PHP array implementation is the primary reason I 
use PHP today.  If you want pseudorandom-ish order back in your userland 
PHP arrays, then you could try using array_rand() or similar.

Keys can also be a mixture of integers and strings.  Most hash table 
implementations require choosing one key type and sticking with that.

The only weakness in PHP's implementation is that there aren't built-in 
userland functions to insert elements before/after specific keys.  Users 
instead have to rebuild the whole array just to insert one element at a 
desired position while maintaining keys and order.  It's occasionally 
useful to do so and rebuilding an array can be an expensive 
memory-churning operation when a much more performant solution is just 
slightly out of reach of userland.

From:

https://github.com/cubiclesoft/cross-platform-cpp

"The detachable node ordered hash is similar to PHP arrays.  It accepts 
both integer and string keys in the same hash, has almost constant time 
insert (anywhere!), lookup, delete, and iteration operations (both 
directions), and, most importantly, maintains the desired order of 
elements."

All the potential benefits of marrying a hash table to a linked list in 
a single paragraph.

-- 
Thomas Hruska
CubicleSoft President

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