From: Alex Martelli <aleaxit@...>
Date: 2003-09-17T02:51:56+09:00
Subject: Re: performance and style advice requested

Hal Fulton wrote:

> Alex Martelli wrote:
>> Simon Strandgaard wrote:
>>    ...
>> 
>>>>def comb(x, y)
>>>>    # combinations of x things y at a time (0 if x<0, y<0, or y>x)
>>>>    result = $_comb_memo[[x, y]]
>>>
>>>                           ^^^^^^
>>>                           ^^^^^^
>>>
>>>                         very slow!!
>>>
>>>Ruby converts it the array into a string.. this takes time!
>> 
>> 
>> Oh my!  I had no idea Ruby suffered under such a handicap wrt to Python
>> (that arrays had to be converted to strings to index into hashes, while
   ...
> Simon is mistaken here. There may be some kind of
> speed hit when storing an array as a hash key, but
> the key is definitely stored as an array.

Ah!  Good to know, thanks -- I was (mistakenly, of course) taking all the 
pronouncements of the c.l.ruby readership as if they came from Ruby
experts -- unless of course corrected by others at the time I got to read
them (I always read news and mail backwards in time to cover for that),
while Simon's remark had been left unchallenged until now.  Still, the
move from [x,y] to x<<16+y did accelerate Ruby a bit (while the same
change slowed Python down a bit) so it does seem the "some kind of speed
hit" may in certain cases be (though not by much) noticeable.


Alex