Re: [Boost-users] [multi_index] modify~~

Subject: Re: [Boost-users] [multi_index] modify~~
From: joaquin_at_[hidden]
Date: 2010-08-02 07:49:51

isjk escribió:
> hi,
>
> now, I have two structures like this,
>   
> [...]
>
> typedef multi_index_container<
>     const channel*,
>     ordered_non_unique<
>        key_from_key<
>           BOOST_MULTI_INDEX_MEMBER(peer, const int, guid_),
>           BOOST_MULTI_INDEX_MEMBER(channel, const peer*, pr_)
>        >
>     >
>   
>> channel_table_pr_view;
>>     
>
> [...]
>
> channel_table_pr_view::iterator ictpv = ctpv.find(guid_);
> if (ictpv != ctpv.end())
> {
>     ctpv.modify(ictpv, _Modify_prop()); // right or not?
> }
>
> struct _Modify_prop{
>     void operator()(channel& cl_)
>     {
>          cl_.prop = rand();
>     }
> };
>
>   

This is not correct: _Modify_prop is passed a reference to the element of
channel_table_pr_view, which is a const channel*, so the right signature
for _Modify_prop::operator() is

  struct _Modify_prop{
      void operator()(const channel*& pcl_);
  };

Due to the const qualifier you won't be able to do the modification, so 
consider
redefining channel_table_pr_view as holding pointers to non-const objects:

  typedef multi_index_container<
    channel*,
    ordered_non_unique<
      ...
  > channel_table_pr_view;

and making the necessary adjustments.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo