Re: [Boost-users] [multi_index] sorted iteration of values

Subject: Re: [Boost-users] [multi_index] sorted iteration of values
From: Joaquín Mª López Muñoz (joaquin_at_[hidden])
Date: 2013-09-04 02:15:24

El 04/09/2013 7:15, Mathieu Champlon escribió:
> Hello,
>
> [...]
>
>     typedef SomeType* First;
>     typedef int Second;
>
>     struct Value
>     {
>         First first;
>         Second second;
>     };
>
>     boost::multi_index::multi_index_container<
>             Value,
>             boost::multi_index::indexed_by<
>                 boost::multi_index::ordered_unique<
>                     boost::multi_index::composite_key<
>                         Value,
>                         boost::multi_index::member<
>                             Value, First, &Value::first >,
>                         boost::multi_index::member<
>                             Value, Second, &Value::second >
>                     >
>                 >,
>                 boost::multi_index::ordered_non_unique<
>                     boost::multi_index::member<
>                         Value, Second, &Value::second >
>                 >,
>                 boost::multi_index::ordered_non_unique<
>                     boost::multi_index::member<
>                         Value, First, &Value::first >
>                 >
>             >
>         > data;
>
> This works, except for the ints iteration based on a given SomeType*
> because I need
> them to be sorted, and they're not, e.g.
>
>     auto range = data.get< 2 >().equal_range( someTypePtr );
>     for( auto it = range.first; it != range.second; ++it )
>         ;
>
> does not iterate in a sorted order.

Use index #0:

     auto range = data.get< 0 >().equal_range( someTypePtr );

In fact, you can get rid of index #2: when using a composite key you
can search by providing only the first m fields of the key, so for
all practical purposes index #2 is redundant with #0.

Joaquín M López Muñoz
Telefónica Digital

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