Howard Hinnant wrote:
On Feb 14, 2005, at 2:52 PM, Jonathan Turkanis wrote:
Howard Hinnant wrote:
I'd definitely like some standard way for a type to declare itself tuple-like. Why didn't it make it into TR1?
I use a version of it here, to allow arbitrary tuple-like types to take advantage of a form of tuple i/o:
http://www.kangaroologic.com/format_lite/libs/format_lite/doc/? path=4.2.5
<nod> I use is_tuple_like too. It was in the original proposal. It got dumped somewhere along the way. I'm not sure why. When tuple was first voted into TR1, enable_if was brand new and pretty exotic. Parts of tuple that benefited from (and depended on) enable_if were dumped. It may be that is_tuple_like got thrown out along with that dump. Imho, tuple did not benefit from that exercise. We get another shot at it for C++0X though. So existing practice that is a little better than TR1 can still help.
FYI, Fusion already has the infrastructure to do that. For instance, MPL sequences are tuple sequences and vice versa. It's a matter of defining some helper classes that implement something akin to MPL's TAG dispatch mechanism. Hence, a user can (in theory) make any form of tuple-like structure play along well. Alas, the TR1 interface is not sufficiently rich to handle all forms of tuple like structures. In particular, get<N> assumes O(1) access, which is obviously not always true. Fusion, like MPL and STL uses iterators as the underlying and unifying concept. Cheers, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net