From: Pit Capitain <pit@...>
Date: 2002-11-20T04:11:24+09:00
Subject: Re: ruby-dev summary 18711-18810

On 20 Nov 2002 at 2:59, Bob Alexander wrote:

> From: "Pit Capitain" <pit@capitain.de>
> 
> > Do you know implementations like (from Ruby CVS)
> > rough/lib/generator.rb? Why do you think these are inefficient?
> 
> I haven't seen that (but I'll definitely take a look). I think
> generators can be implemented efficiently. In my experience with
> generators in other languages, the time efficiency is good enough, and
> depending on the underlying language implementation, they can be
> costly of space since in some implementations they require their own
> contiguous stacks (almost like threads -- to support suspended C
> stacks in the underlying C code).

Hi Bob,

thanks for the clarification. I wasn't sure what you meant by 
"inefficient". The (generic) iterator implementations presented so 
far seem to be at least space-inefficient, because they either create 
arrays or use threads/continuations.

> If Ruby has an efficient generator capability, it would be a good way
> to implement "zip" without the space cost of creating an entire copy
> of all of the pointers in all involved sequences.

Not yet, but Matz seems to be working on it.

> BTW, I have quite a bit of experience with languages that support
> generators (...)
> I attached a small experimental Ruby class I
> wrote a long time ago that implements something like this. The
> implementation uses threads and queues, so is not very efficient.

But the code is a nice read, thanks a lot.

> However, an API of this sort could possibly be implemented efficiently
> at a lower level.

If I understood Matz correctly he's working on a low-level 
implementation of zip, but doesn't like external iterators (sigh).

Regards,
Pit