With apologies for the late review - I think the extension to type_traits should be accepted into Boost, it's a needed and useful extension to the existing library. I think the comments to the effect that the default for the return value should be changed from void to "dont_care" or some such type are correct. I'm not much concerned whether it's possible to check for void return types as I can't think of a use for that ;-) Possibly the most controvertial part of the library is the names used for the traits classes - I think the existing names used by Frédéric are consistent, and I would be perfectly happy with them - but I'm not against changing them either if there are better options. I notice there are some non-ASCII characters in the header file copyrights - I can't remember off hand whether we still prohibit that, but I suspect we do (with apologies to all non-English folk!!) I realise this is a bit of a short review, but I can't think of anything else to say at present.... just get 'em in Boost ;-) Regards, John.