Nick Stokes <randomaccessiterator <at> gmail.com> writes:
Sorry for being vague about versions. This was with Boost 1.49. Both Visual Studio 2012 and 2013 generates the warning. Clang 3.5.0 and g++ 4.7.2 do not. They all compile fine at the end.
Also I just tried with Boost 1.56. There is no warning in either compiler! Strangely, the result_type typedef in key extractor is still non-& in this version. Perhaps Boost.Range changed...
Please don't top-post: http://www.boost.org/community/policy.html#quoting Thank you! So, to sum up the top-posted chain of posts of yours, boost::multi_index::member<Class,Type,PtrToMember> publicizes its result type as typedef Type result_type; yet its call operator overloads return Type& or const Ttype&, and this results in some warnings in VS 12 / Boost 1.49 when used in combination with boost::adaptors::transform. So, whatever the problem is, it does not belong in Boost.MultiIndex, since member merely defines result_type in accordance with the requirements of the Key Extractor model: http://www.boost.org/libs/multi_index/doc/reference/ key_extraction.html#key_extractors I mean, defining result_type in whatever way (or not defining it at all) is not an error per se; it is Boost.Range assumptions on this typedef that might be problematic. Unfortunately, the documentation for boost::adaptors::tranform(rng,fun) http://www.boost.org/libs/range/doc/html/range/reference/ adaptors/reference/transformed.html do not mention what the requirements on fun are, whether it is mandatory that a result_type be present and how this is handled by Boost.Range. I suggest you initiate a new discussion with [range] in the subject line showing the problem you found. I suspect this is related to boost:result_of http://www.boost.org/libs/utility/utility.htm#result_of which Boost.Range seems to use internally, but only the author can tell. Also, if the problem does not show in Boost 1.56 you might be encouraged to simply upgrade and move on. Joaquín M López Muñoz Telefónica