Re: [Boost-users] [multi-index] No constructor that takes allocator only

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2008-01-30 16:36:07

----- Mensaje original -----
De: Michael Fawcett <michael.fawcett_at_[hidden]>
Fecha: Miércoles, Enero 30, 2008 9:23 pm
Asunto: Re: [Boost-users] [multi-index] No constructor that takes 
allocator only
Para: boost-users_at_[hidden]

> On Jan 30, 2008 3:06 PM, Joaquin M Lopez Munoz <joaquin_at_[hidden]> 
wrote:
> > I'm holding your proposal in my todo list, but I have to think
> > it over a bit.
> 
> I trust you'll come to the best decision.  Really it comes down to
> what customization point is more often used (since the interface will
> favor that), and that is invariably the compare parameter.  My
> original suggestion should probably be ignored in favor of keeping
> with the set interface.

It's possible that both ctors could be provided, because
the situation for multi_index_container is not entirely equivalent
to that of std::set. I'll keep you informed.

> As an aside, does Boost.MultiIndex model any existing Boost concepts
> (e.g. AssociativeContainer)?
> 
> http://www.boost.org/libs/concept_check/
> reference.htm#container-concepts
> I found some documentation here (
> http://www.boost.org/libs/multi_index/doc/tutorial/
> techniques.html#emulate_std_containers
> ) , that hints it might, but no explicit mention of modeling 
Concepts.

Well, the answer is, in general, no. multi_index_containers
certainly model Container, but nothing beyond that (Sequence
or AssociativeContainer) for a variety of possible reasons:

* Index #0 (as you know, multi_index_containers inherit the
public interface of that index) might have some slight deviations
from the interface of the corresponding container: for instance,
sequenced indices are like std::lists, but push_back() and other
memfuns have a different signature.
* Elements are immutable (unlike standard Sequences).
* Insertion semantics depends on every and each index comprising
the multi_index_container, not only index #0.
* Same for operation complexities: insertion, erasure, etc.

So, you can get close to modelling a given Concept, but
not strictly there. About the only exact match you've got is
the emulation of std::set described at the section you refer
to above.

HTH,

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo