Re: [Boost-users] Boost.multi_index: how to use a member function instead ofoperator<()?

Subject: Re: [Boost-users] Boost.multi_index: how to use a member function instead ofoperator<()?
From: Alan M. Carroll (amc_at_[hidden])
Date: 2009-02-23 15:43:27

I don't think you can use a method directly (Boost.bind won't work because you need a type, not a functor instance). I would just create a nested functor class to call Object::fn. Here is an example, compiled on Boost 1.38.0, gcc 4.3.2.  I would put real code in Object::fn(), though. There may be an MPL metafunction to do the equivalent of what the struct ordering does.

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

class Object {
public:
    struct FN_INDEX;
    bool fn(Object const& that) const { return true; }
    struct ordering : public std::binary_function<Object const&, Object const&, bool> {
        bool operator () (Object const& lhs, Object const& rhs) const {
            return lhs.fn(rhs);
        }
    };
};

using namespace boost;
using namespace boost::multi_index;

typedef multi_index_container
    < Object
    , indexed_by
        < ordered_unique < identity < Object > >
        , ordered_unique
            < tag<Object::FN_INDEX>
            , identity<Object>
            , Object::ordering
            >
        >
    > container;

container TheContainer;

At 01:03 PM 2/23/2009, you wrote:
>Hi,
>
>I want to use in index based on a member function that returns a bool if
>an element is smaller than an other element like operator<. But I cannot
>find how to do that.
>
>e.g.
>
>using namespace ::boost;
>using namespace ::boost::multi_index;
>
>class Object{
>  bool operator<(const Object& rhs) const;
>  bool fn(const Object& rhs) const;
>}
>
>struct FnIndex{};
>
>typedef multi_index_container<
>Object,
>indexed_by      <
>ordered_unique< identity< Square > >, // this uses operator<(const Object&) I believe?
>ordered_unique< tag< FnIndex >, ?????????????? >
>>
>> ObjectContainer;
>
>If this possible, what should I use in the place of ?????????