[Boost-users] [unordered] Merging unordered maps

I have a performance hotspot when merging a few unordered_maps of the same type into a master unordered_map (also of the same type) Currently I am doing Foreach( auto const& submap ,submaps ) Master.insert( submap.begin() , submap.end() ); This seems to be somewhat wasteful because the insert is (I think) computing hashes that the submaps already "know". Can I improve on this - without changing Boost? - without changing the boost interface, but changing the implementation (eg specialising the insert for certain iterator types)? - some more intrusive change? If the second or third option, would the maintainer be willing to consider merging the change into Boost proper? Thanks, Pete