Re: [Boost-users] Request for conditional index feature in boost multi-index

22 Dec 2010

      Gokulakannan Somasundaram escribió:
...
Hi,
   First of all thanks for the great library, which had reduced our 
development
   time by a lot. 
   In boost multi-index, we currently have almost all the indexing 
concepts
   integrated. Hence i am requesting for a new feature called 
conditional indexes,
   where in an index/view inside multi-index will only index a portion 
of the
   entries inside the entire multi-index(Say something that satisfies 
a functor).
   This is in resemblance to the partial indexes in Postgresql.  
   I feel that would provide elegant solutions to lot of issues 
without forming
   round about solutions. For example i have a requirement where in 
there are
   two sets of data with the same search criteria, but different 
eviction criteria
Say i have two sets of data with same search condition, but one set 
needs a
MRU(Most Recently Used) list of 100 and the other set requires a MRU 
of 200.
Say the entry is like this
[...]
The general request (composing partial indices to cover the whole 
sequence) is
interesting and a considered it some years ago, though I never found the 
time
to implement it (and I'm suspicious it might be a little too "smart" for 
the general
public).

In any case, I think you can solve your particular problem without that 
feature
in a convenient manner. Please see the attached example and report whether
it satisfies your needs.

Best regards,

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

#include <algorithm>
#include 
#include 
#include 
#include 
#include <iostream>
#include <iterator>
#include <string>

using namespace boost::multi_index;

struct student
{
  student(int num,char sex):num(num),sex(sex){}

  int  num;
  char sex;

  friend std::ostream& operator<<(std::ostream& os,const student& s)
  {
    os<<"("<,
      hashed_unique >
    >
...
student_list;
public:
  typedef student_list::iterator iterator;

  student_mru_list(std::size_t max_male,std::size_t max_female):
    max_male(max_male),max_female(max_female),
    size_male(0),size_female(0){}

  void insert(const student& s)
  {
    bool is_male=(s.sex=='m');
    std::size_t& size    =is_male? size_male   :size_female;
    std::size_t  max_size=is_male? max_male    :max_female;
    iterator     it      =is_male? male_begin():female_begin();

    std::pair p=sl.insert(it,s);
    if(!p.second){             /* duplicate item */
      sl.relocate(it,p.first); /* put in front */
    }
    else{
      ++size;
      if(size>max_size){ /* keep the length bounded */
        sl.erase(is_male?male_end()-1:female_end()-1);
        --size;
      }
    }
  }

  iterator male_begin(){return sl.begin();}
  iterator male_end(){return male_begin()+size_male;}

  iterator female_begin(){return male_end();}
  iterator female_end(){return sl.end();}

  iterator begin(){return male_begin();}
  iterator end(){return female_end();}

private:
  student_list sl;
  std::size_t  max_male,max_female;
  std::size_t  size_male,size_female;
};

void dump(student_mru_list& sl)
{
  std::copy(sl.begin(),sl.end(),std::ostream_iterator<student>(std::cout));
  std::cout<

Re: [Boost-users] Request for conditional index feature in boost multi-index

joaquin＠tid.es