Re: [boost] [multi-index?] Advice about publicizing capacityforsets/vectors

From: Joaquín Mª López Muñoz (joaquin_at_[hidden])
Date: 2007-07-18 02:30:18

Hello Daryle,

Daryle Walker ha escrito:

> I was thinking of using a multi-indexed container as part of an
> implementation of another container.  The final container will have an
> interface like a set, but internally the elements sometimes have to be
> accessible via random-access iteration[1].  Implementing with a straight
> set would limit me to bidirectional iteration, which will slow down
> internal operations that need random access.
>
> The internal multi-index container would have set and vector aspects,
> i.e. ordered-unique and random-access index specifiers.  Even though the
> external interface will be like a set, should I have publicize the
> vector-like operations "capacity" and "reserve"?  Will reserving
> capacity help in the ordered-unique part of any insertions?
>

Yes, reserving will gain you some performance even if insertions are made
through the ordered_unique index --take into account that inserting through
any index will also affect all other indices behind the scenes.

>
> Alternatively, is there a better way to implement a set w/ random-access
> iteration besides this multi-index idea?
>

I hope there isn't :) Seriously, Boost.MultiIndex is designed to be as compact
and efficient as possible, so it's probably an optimum choice for your problem
with respect to memory usage and performance. As for the resulting user
interface, it may not suit your particular needs, in which case you'll have to do
some wrapping work over the core multi_index_container.

Best,

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo