new Type[count] takes too much?

[Jonathan M Davis]

On Thursday, October 31, 2013 23:06:22 Namespace wrote:
> On Thursday, 31 October 2013 at 09:53:39 UTC, Jonathan M Davis
> 
> wrote:
> > On Thursday, October 31, 2013 10:15:51 Namespace wrote:
> >> I'm sure we had already this conversation but I don't find the
> >> thread.
> >> 
> >> T[] buffer = new T[N]; assumes more space than stated (in
> >> average
> >> 2010 elements more. See: http://dpaste.dzfl.pl/af92ad22c). It
> >> behaves exactly like reserve and that is IMO wrong. If I
> >> reserve
> >> memory with buffer.reserve(N), I want to have at least N
> >> elements. That behaviour is correct. But if I use new T[N] I
> >> mostly want exactly N elements and no extra space.
> >> 
> >> Thoughts?
> > 
> > You're making the assumption that it would be normal to not
> > want to then
> > append to something you allocated with new T[N], and I don't
> > think that that's
> > a valid assumption.
> 
> I disagree. If I want to append I use reserve and I think that is
> the most common approach.

I would fully expect that most people don't bother with reserve or capacity 
and that they simply create the array at whatever size they create it at and 
then append to it without worrying about reserve. But we'd have to get real 
data on that to know for sure one way or the other.

Certainly, most folks who are focusing on append performance seem to use 
Appender, and for the most part, I would suggest that anyone using reserve 
should be using Appender instead.

- Jonathan M Davis