Eric Friedman wrote: > I am a bit uneasy about any proposal making adding MPL sequence semantics > to an otherwise-typical value type. If such proposals are implemented, I > see a significant ambiguity problem arising in generic code: given a type > T that is an MPL sequence, should we treat it as a sequence or as a value > type? > > In particular, if we were to implement boost::tuple as an MPL sequence, > the following code would seem to me quite unclear insofar as its intended > behavior: > > typedef mpl::list<int, std::string> some_types; > typedef boost::tuple<int, std::string> some_tuple; > > typedef boost::variant<some_types> v1; // ok, unambiguous > typedef boost::variant<some_tuple> v2; // ambiguity!? > > It seems clear that objects of type v1 should behave equivalently to > boost::variant<int, std::string>. However, if boost::tuple were an MPL > sequence, it seems less clear whether objects of type v2 should behave > likewise or instead as a variant holding a 2-tuple. > > Thus, this question is of particular importance for boost::variant. But > also, I imagine, it is important for any other type implementing a > pseudo-variadic template interface as I intend for the final release of > variant (which is coming, by the way). > > Input?
I agree. -- Alexander Nasonov Remove minus and all between minus and at from my e-mail for timely response _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
