Re: simple List index question

[Rick Riolo]

Thanks for the info.

re 
> position access will be much faster.  If you want fast random access  
> today, the only way to get it is to allocate your own array of id pointers
> and index that directly in C.

...that's how I got started on trying to subclass List
(so I could have my own local array of pointers into it,
and use that for random access.

- r


Rick Riolo                       address@hidden
Program for Study of Complex Systems (PSCS)
1061 Randall Lab     University of Michigan
Ann Arbor MI 48109-1120
http://pscs.physics.lsa.umich.edu/rlr-home.html

On Mon, 20 Nov 1995, Roger M. Burkhart wrote:

> Date: Mon, 20 Nov 95 14:40:23 CST
> From: Roger M. Burkhart <address@hidden>
> To: address@hidden
> Cc: address@hidden
> Subject: Re: simple List index question
> 
> > I just want to check to be sure I am using 
> > List indexing correctly.  Is the basic idea:
> > 
> >     id index, other;
> >     index = [siteNbors begin: xZone];
> >     for ( other=[index next]; other; other=[index next] ) {
> >     [other calcE];
> >     } 
> >     [index dropFrom: xZone];
> 
> Yes, this is fine.  I usually use a while loop rather than a for loop,
> like this:
> 
>   index = [siteNbors begin: xZone];
>   while ( (other = [index next]) ) [other calcE];
>   [index dropFrom: xZone];
> 
> (The extra parentheses around the assignment used as a while condition are
> needed to suppress a gcc warning under -Wall.)
> 
> > As I understand it, when I dropFrom the index,
> > I'm just getting rid of it, not anything in the
> > siteNbors List itself...is that right?
> > 
> > Also, am I right that the index and the original List
> > don't have to be in the same zone?
> 
> Yes on both.  An index is often allocated in a scratch zone for local,
> temporary use and dropped as soon as it is no longer needed.  It is intended
> to be a very low overhead object for collection traversal.  It always does
> a good job of sequential traversal (forward or backward), but random position
> access (for example, to a random position via [index setOffset: iOffset])
> depends on the underlying implementation.  For the current list, this is
> no better than sequentially traversing up to the requested offset.  For
> other list implementations and for Array (both to be provided) random
> position access will be much faster.  If you want fast random access
> today, the only way to get it is to allocate your own array of id pointers
> and index that directly in C.
> 
> Roger
>