Re: [Boost-users] [boost::multi-index] improvement suggestion

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2007-08-24 14:35:19

----- Mensaje original -----
De: Ovanes Markarian <om_boost_at_[hidden]>
Fecha: Martes, Agosto 21, 2007 1:27 pm
Asunto: Re: [Boost-users] [boost::multi-index] improvement suggestion
Para: boost-users_at_[hidden]

> Joaquin,
> 
> thanks for your reply. I have to think about your suggestions. Some 
> ideaswhich come up to my mind now are:
> 1. Locator is clearly a better choice, but not always. In some use 
> cases you might find a range if a container allows multi-indexed
> values. In this caseone would need to make second search to find
> subsequent values??? 
> Or miss them at all...

I take you meant "duplicate values" rather than "multi-indexed values",
right? If so, yes I agree with you a range is the proper object to
return, but you'd have to use equal_range instead of find.

> 2. In the example with:
> boost::iterator_range<std::set
>   <std::string>::const_iterator> r=
>     find_range(...);
> 
> The class value_retrieval contains a result_type which provides the 
> shortcut to iterator_range<...>

Correct, this'd make the syntax terser.

> 3. My idea in using iterator range relies on fact that one can 
> retrieve a
> valid or invalid range and operate on it within one search. Your 
> idea with there_exists requires a second search to retrieve the
> value. Since a typical use case would be:
>
> if(there_exists(some_container, "some_key"))
>    some_value = *some_container.find("some_key");
> 
> and that is not so efficient as:
> 
> iter_range range = find_range(some_container, "some_key");
> if(range)
>   some_value = range.front();

OK, then a locator seems to me to provide a nicer syntax
in one single call than your first approach based on ranges.
My point is only that your approach has a nice interface
for checking if the value exists but not so much for
accessing the actual value.

> I will think about other suggestions and mail them later
> in ;)

Thank you for using Boost.MultiIndex and thinking up ways to
improve the experience it provides.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo