Re: [Boost-users] Collecting boost multi-index meta data

Subject: Re: [Boost-users] Collecting boost multi-index meta data
From: Gokulakannan Somasundaram (gokul007_at_[hidden])
Date: 2011-03-25 07:22:40

Thanks a lot. I think this should do.

Thanks,
Gokul.

On Thu, Mar 24, 2011 at 7:13 PM, <joaquin_at_[hidden]> wrote:

> Gokulakannan Somasundaram escribió:
>
>  Hi Joaquín ,
>>         I am extremely sorry, i missed your mail. First of all thanks
>> a lot for replying.
>>
>
> No problem. Please don't top-post:
> http://www.boost.org/community/policy.html#quoting
>
>  I have fixed the issue for now. But i am actually explaining the issue
>> i had. Please take a shot at it.
>>        Say i have an object and i have created multi index on some
>> members of the object. Now since,
>> this is being used in a multi-threaded code, i will acquire a mutex on
>> the whole multi-index, only if i have
>> updated those attributes involved in the multi-index build. Else i
>> won't take the mutex.
>>        Now my problem is, i have multi-indexed many such classes.
>> what is the best way to check whether
>> the updated attribute is part of multi-index. Currently we have
>> written a python code which scans the C++
>> files and creates a list of attribute numbers ( each member attribute
>> has a number associated with it ).
>> Whenever there is an update, we check against the list produced by the
>> python code in C++.
>>        My question was if there is a way to do this within C++ itself.
>>
>
> If we had the following metafunction to check whether a particular
> key extractor is used with a multi_index_container or not:
>
>  template<typename KeyExtractor,typename MultiIndexContainer>
>  struct is_key_extractor_of{};
>
> then it is easy to know at compile time if a particular member of a class
> is
> referenced by a member<...> key extractor (composite keys are harder and
> left as an exercise to the reader):
>
>  struct A
>  {
>    int a,b,c,d,e,f;
>  };
>
>  typedef multi_index_container<
>    int,
>    indexed_by<
>      ordered_unique<member<A,int,&A::a> >,
>      sequenced<>,
>    >
>  > multi_t;
>
>  BOOST_MPL_ASSERT    ((is_key_extractor_of<member<A,int,&A::a>,multi_t>));
>  BOOST_MPL_ASSERT_NOT((is_key_extractor_of<member<A,int,&A::e>,multi_t>));
>
> Full code provided in the attachment. Does this help to implement your
> scenario?
>
> Joaquín M López Muñoz
> Telefónica, Investigación y Desarrollo
>
>
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