Re: [boost] [multi_index] Question about 'modify'

From: Joaquín Mª López Muñoz (joaquin_at_[hidden])
Date: 2004-08-30 11:43:30

Vladimir Prus ha escrito:

> I have a question about the 'modify' method of ordered indexes in the
> multi_index library. I have an iterator obtained from an ordered index and
> would like to modify the pointed element. I'm pretty sure that the
> modification won't change the order, won't create collisions and so on.
>
> The documentation suggests to use either 'replace', or more efficient 'modify'
> method. Why can't I do the following:
>
>      typedef variables_t::nth_index<1>::type index_t;
>      index_t& index = variable_declarations.get<1>();
>      index_t::iterator existing = index.find(vd);
>      const_cast<Variable_declaration&>(*existing)
>                         .make_external();
>

You can do this as long as you're 100% sure there won't be collisions
or reorderings. This is no different to const_casting away an element in a
std::set: if you know what you're doing, well, it's OK. That said,
using replace or modify keeps you on the safe side.

Best,

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo