Re: [Boost-users] [MultiIndex] Indexing integers

Subject: Re: [Boost-users] [MultiIndex] Indexing integers
From: Sensei (senseiwa_at_[hidden])
Date: 2014-07-20 03:56:11

Thanks Joaquin, I've played with your example and I find it very useful! 
Now the appetite grew and combining your example with the custom key 
extractor docs you provided, I am trying to move to a single class with 
a multi index member. However, I cannot compile it.

My attempt is now to use a 128bit integers, and extract MSB/LSB as 
before. The difference is using a const member function. Of course, I've 
specialized std::less for my type.

The errors are puzzling to me. Here they are:

== LOG ==
In file included from Data.h:15:
/usr/local/include/boost/multi_index/mem_fun.hpp:42:50: error: member 
pointer refers into non-class type 'unsigned __int128'
template<class Class,typename Type,Type 
(Class::*PtrToMemberFunction)()const>

Data.h:42:32: note: while substituting prior template arguments into 
non-type template parameter 'PtrToMemberFunction' [with Class = unsigned 
__int128, Type = unsigned long long]
             ordered_non_unique<const_mem_fun<__uint128_t, uint64_t, 
&soData::msb>>,
 
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Data.h:42:83: error: expected a type
             ordered_non_unique<const_mem_fun<__uint128_t, uint64_t, 
&soData::msb>>,
 
            ^
/Users/sensei/Documents/Projects/sparql/Sparql/Sparqlo/soData.h:45:5: 
error: expected a type
     > soDataStorage;
     ^
== END ==

I must confess I cannot understand what type it expects.

 From the documentation I see that I need in const_mem_fun<> in order, 
the input type, the output type, and the address of a member function, a 
const member in my case.

    // sort by less<int> on name_length()
     ordered_non_unique<
       const_mem_fun<employee,std::size_t,&employee::name_length>
     >

I believe less<> isn't a problem, since it should work on 128bit 
integers with my specilization... I think!

Can anyone help me?

Thanks & Cheers!

#include <boost/multi_index_container.hpp>
#include <boost/multi_index/mem_fun.hpp>
#include <boost/multi_index/ordered_index.hpp>

#include <functional>

using namespace boost::multi_index;

namespace std {
     template<>
     struct less<__uint128_t>
     {
         bool operator()(const __uint128_t& x, const __uint128_t& y) const
         {
             return x < y;
         }
     };
};

using namespace boost::multi_index;

class Data
{
public:
     Data();

     uint64_t msb(__uint128_t storage) const
     {
         return static_cast<uint64_t>(storage >> 64);
     };

     uint64_t lsb(__uint128_t storage) const
     {
         return static_cast<uint64_t>(storage & 0xFFFFFFFFFFFFFFFF);
     };

private:

     typedef multi_index_container<
     __uint128_t,
         indexed_by<
             ordered_non_unique<const_mem_fun<__uint128_t, uint64_t, 
&Data::msb>>,
             ordered_non_unique<const_mem_fun<__uint128_t, uint64_t, 
&Data::lsb>>
         >
     > DataStorage;
};