Hello, map.hpp defines two overloads for adaptors::values, one for StdPairRange& and another for const StdPairRange const& rng. On the other hand, there is just a single adaptors::keys which takes StdPairRange const&. In particular, the code below will not compile: boost::find_if( boost::adaptors::keys(rng), SomePredicate() ).base()->second=NewValue(); Therefore, I would propose an adaptors::keys(StdPairRange& rng) overload similar to adaptors::values(StdPairRange&). Iterators of the returned range shall have a mutable base iterator. Further, iterators of the returned range should have a reference type of range_value<StdPairRange>::type::first_type& , so the elements in keys are mutable where StdPairRange admits this. Regards, Valentin -- Valentin Ziegler | vziegler@think-cell.com Software Engineer think-cell Software GmbH | Chausseestr. 8/E | 10115 Berlin | Germany http://www.think-cell.com | phone +49 30 666473-10 | US phone +1 800 891 8091 Amtsgericht Berlin-Charlottenburg, HRB 85229 | European Union VAT Id DE813474306 Directors: Dr. Markus Hannebauer, Dr. Arno Schoedl