From: Hal Fulton <hal9000@...>
Date: 2003-09-16T02:38:26+09:00
Subject: Re: performance and style advice requested

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
> Python can use "tuples", its equivalent of frozen arrays, for that) --
> then I must definitely be very sparing in using hashes with multi-dim
> indexes in Ruby, at least in any bottleneck.  Thanks!  Just the kind of
> things I'm trying to learn (I don't remember noticing any such caveat
> in Thomas and Hunt's excellent book).

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.

Hal