Lately I've been exploring boost/fusion for a project which I have been thinking about for 25 years. I believe that this might be the tool to do what I want. In the course of my experiments with this library and it's associated documentation, I've been interested in understanding the libraries "concepts" (e.g. AssociativeSequence, etc) and the relationship if any to the boost concept library. To try to be more clear, when I see something in the documentation like "AssociativeSequence", I'm sort of hoping/expecting to write into my code something like template<typename S> struct my_type { ... BOOST_CONCEPT_ASSERT(( <AssociativeSequence<S> > )); ... }; But it seems that I can't do this. Why is this? a) Can I indeed write something like this if I include some specific headers that I haven't found? b) Should I be using some other concept checker such as something in MPL c) Am I wrong about thinking that it would be useful to have this? That is, is there some reason why I shouldn't expect to find this? In poking around, I don't find a lot I'm expecting to find. For example, I'm sort of expecting to find: boost::std::concepts { ... concept checking classes for STL } and something similar for all or most of the libraries who make extensive usage of "concepts" in their documentation. When I so grep for files which contain BOOST_CONCEPT (to catch BOOST_CONCEPT_ASSERT, etc.. I get the following: bash-3.2$ pwd /cygdrive/c/BoostRelease/boost bash-3.2$ grep -l BOOST_CONCEPT * */*.hpp concept_archetype.hpp concept_check.hpp concept/assert.hpp concept/requires.hpp concept/usage.hpp concept_check/borland.hpp concept_check/general.hpp concept_check/has_constraints.hpp concept_check/msvc.hpp graph/bron_kerbosch_all_cliques.hpp graph/buffer_concepts.hpp graph/graph_concepts.hpp graph/graphviz.hpp graph/metric_tsp_approx.hpp graph/stoer_wagner_min_cut.hpp graph/tiernan_all_cycles.hpp graph/transitive_reduction.hpp icl/closed_interval.hpp icl/continuous_interval.hpp icl/discrete_interval.hpp icl/interval_base_map.hpp icl/left_open_interval.hpp icl/map.hpp icl/open_interval.hpp icl/right_open_interval.hpp iterator/iterator_concepts.hpp range/concepts.hpp bash-3.2$ which suggests to me that this idea is only implemented in graph, icl, iterator and range libraries. Is there a reason for this, or is that it just hasn't been done. If it's the latter, is there a reason I don't see anyone on the requesting that libraries include concept checking classes. Also, reviewers don't seem to mention the lack of these classes in the code - though they complain about it if it's missing from the documentation. After sort of struggling with the whole concept concept, I'm think I'm coming to appreciate it's utility and maybe it's necessity. But given that no one seems to miss it in the boost libraries, I'm concerned that I'm still not getting it. Robert Ramey