Re: Passing buffers to function in elisp

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> This is a typical a source of unnecessary O(N²) complexity: the above
>> line takes O(N) time, so if you do it O(N) times, you got your
>> N² blowup.  You're usually better off doing
[...]
> I replaced vconcat with push.  However it did not have a significant
> effect (measured with Emacs memory profiler).  Perhaps the chunks were
> quite small after all.

That's usually the case, indeed.

> In complexity speak, with small N one usually
> does not need to worry about quadratics.

But: it's rare to be sure that N will *always* be small :-(

> I also tried to replace with-temp-buffer forms (such forms are called
> hundreds of times) with a static buffer for holding temporary data.  It
> produced mixed results.  In some limited settings, memory savings were
> considerable, but in some others cases it blew up memory usage.  I
> cannot explain why that happened.  But it seems safest to stick to
> with-temp-buffer.

`with-temp-buffer` is fairly costly, but to the extent that it's pretty
much a constant cost it shouldn't [known on wood] bring surprises in
unexpected circumstances, so if it's fast enough it's a good choice.


        Stefan