on Sun Feb 22 2009, "Vladimir Batov" <batov-AT-people.net.au> wrote:
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;
Well, if the user-defined formatter is not part of the type of the converter (e.g. encoded in a template parameter) then you will indeed have some issues because there is a type-erasure boundary to cross. You could do it (Daniel did it when he extended Boost.Parameter to interoperate with Python), but I doubt you'd find Boost.Parameter to be a trivial drop-in solution in that case. Maybe it could be easily extended to do what you need, though. I don't know how close your use case comes to the Python use-case. Certainly, the interface you show above is easy enough to achieve. -- Dave Abrahams BoostPro Computing http://www.boostpro.com