Before I write a review, I have a couple of questions that are the outgrowth of having been using mp11 since some time after the first two articles of Peter’s. That should suggest I generally like the library, which I do. Nevertheless, in my code, I have found need for the following additional metafunctions: - mp_map_keys: creates a list of keys from a map - mp_is_map: type trait to determine whether a type is a map, i.e., has a unique set of keys - mp_is_set: type trait to determine whether a type is a set, i.e., has unique elements Is there a reason that support for such functions should not be in the library? I have also found need for a metafunction that takes a map and a set of keys and returns a map with only elements with the selected keys. This is perhaps more specialized, but I can also see a general use case. I would appreciate your thoughts on these functions. Thanks. Cheers, Brook