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 ?????????