I am not sure Boost.Parameter can be applied for the Boost.Convert task in question (although Andrey is really pushing for it :-)). However, I must say it is a very nifty thing you've come up with. I am thinking really hard where I might use it. :-)
This seems to evade your earlier statement a bit:
If you tell me that the user can make Boost.Convert understand that new parameter without modifying Boost.Convert, I'll be first to abandon manipulators in their favor.
Dave, it probably might well appear this way... but I am not really trying to evade anything. The thing is that Boost.Parameter is a new thing to me and I have not seen much code using it. So, I am still not sure how to plug it into Boost.Convert (sorry for using the name I know it's not part of Boost, I just need to refer to it somehow quickly). Now I understand that Boost.Parameter allows me to call convert<string, int>(str, some_user_defined_param = ...); As I understand Boost.Convert does not know and does not make use of "some_user_defined_param" but takes it in using ArgumentPack. How then does the parameter make it to some user-defined formatter? Maybe it is because I am still thinking in terms of manipulators -- a user writes his own and plugs it into Boost.Convert as convert_to<int>(str) >> std::hex; How do we do that with Boost.Parameter? Should we write/specify some kind of Boost.Parameter-aware manipulator? What the signature then might be? Is there some other way? convert<string, int>(str, default_ = -1, throw_ = false); indeed looks trendy and I probably could extend the convert() interface that far. However, I understand Andrey's interest is in the user providing his own keyword (like throw_on_out_of_range_) so that it could be used somewhere for formatting. Where and how that's what I am having difficulty with (due to no experience with Boost.Parameter). V.