Re: [Boost-users] [multi_index] function to force to recreate indexes?

----- Mensaje original ----- De: Boris Fecha: Miércoles, Febrero 21, 2007 8:29 pm Asunto: Re: [Boost-users] [multi_index] function to force to recreate indexes? Para: boost-users@lists.boost.org

On Wed, 21 Feb 2007 20:37:42 +0200, Joaquín Mª López Muñoz wrote:

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[...]I'm almost regretting having posted this trick :) since all of this is really completely unguaranteed behavior --so if you can do things in a safer fashion please go that way.

I won't use the trick but the code you posted before. :) But your proposal with the null_modifier looks like it can be implemented in a refresh() method of the multi_index_container and thus used by everyone to recreate indexes reliably?

Even the null_modifier thing is not guaranteed behavior; but even overlooking that fact, you can't use it to implement refresh(). I guess you have something like the following in mind: void refresh() { for(iterator it=begin();it!=end();++it){ modify(it,null_modifier()); } } right? This has two problems, the latter of a fundamental nature: 1. Since elements are repositioned as you traverse them, you can skip elements, visit repositioned elements twice, etc. 2. modify() is not guaranteed to work in this context, as all the elements are shuffled, and modify() assumes that the only displaced element (at most) is the one being directly dealt with. This is not a theoretical limitation, if you try to do it chances are that the program crashes. At the end of the day, the problem is not whether we can have a reliable implementation of refresh(): you enter into the realm of undefined behavior once you modify an element externally to the container. By the time you are to call refresh(), you have already performed an illegal action. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo