I'd like to replace a bidirectional mapping (2 std::maps so far) with Boost.Bimap. Being based on Boost.MultiIndex I hope there are some space savings there (also I could not find specifics in the docs). I have run into some questions/issues that I hope someone can shed light upon. i) I insert a name/value pair like: typedef boost::bimap<std::string, int> MyBimap; MyBimap myBimap; bool ok = myBimap.insert( typename MyBimap::value_type(name,val) ).second; Is it possible (w/o checking afterwards) to find out *why* the insert failed? (It might be a duplicate on the left or the right side. I want to print a helpful debug message...) ii) I would like to use a Bimap in a templated class: Works ok. When I try to tag the bimap, I get the following errors (using gcc 4.1.2) error: expected primary-expression before 'template' error: expected `;' before 'template' (The errors are the calls to by<country>() // wrapped tagged_simple_bimap.cpp from the Bimap docs in a template class: template<typename T> class X { typedef bimap < tagged< std::string, country >, tagged< T , place > > results_bimap; ... }; (I have attached the modified example.) Tagging works if the bimap definition does contain templated types. Any ideas what I am doing wrong? iii) I need the order of my insertions at one place in my code. Do I lose lookup efficiency (on the left side) when I declare my map as: typedef bimap <vector_of<std::string>, int> (My (bi)map is initialized once and then used for lookups only. Is it better in that case to store the insertion order in a separate vector? Or should I go for the more awe-inspiring Boost.Multimap if I want a Bimap (with efficient lookup) *and* have access to the insertion order? ) iv) What is the difference between: typedef bimap< std::string, int, list_of_relation> ...; and typedef bimap< vector_of<std::string>, int> ...; Thank you for a helpful library (collection). Christoph