Eric Niebler <eric <at> boost-consulting.com> writes:
Stefan Strasser wrote:
you might be interested in this document from the new c++0x mailing:
http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1796.html
for the naming discussion, proposed syntax is for(int i : vec) (personally I don't care if it's called BOOST_FOREACH or BOOST_FOR)
I've questioned in the past if it is expected behaviour to do "hoisting". the proposal does.
"4 Making a custom type work with the for loop" may also be interesting to make the BOOST_FOREACH extension mechanism similar.
This essentially *is* the BOOST_FOREACH extension mechanism, or what it would be if we had auto and decltype today.
I'm glad to see foreach moving ahead in the committee. Obviously, I'm of the opinion that C++ needs this.
This proposal is a good start, but it seems to take quite a bit for granted. It depends on the auto function(...) -> decltype(...) syntax. It depends on rvalue references. It assumes that the Boost.Range begin() and end() functions exist in std namespace (and I'm not aware of a proposal to add those). Perhaps the proposal should discuss alternate designs should certain features not make it into the language.
yeah, that is always a concern. I do think it is likely that the machinery I use in the proposal will be avaiable in C++0x (please not this is my personal opinion)
It also relies on ADL of the begin() and end() functions, even though we decided, after a very lengthy discussion on Boost.Users, that this isn't the way to go, IIRC.
it was decided that intrusive/automatic ADL from a qualified call to boost::begin should *not* do ADL. that is different from what I propose in the proposal. In Lillehammer I started out with not using ADL, but it just didn't feel right; I gave it a lot of thought before I changed it and tried to compile some examples where ADL must find functions defined after the template, but before the instantiation; it worked as I hoped, so I don't see any good reason for not letting us use ADL.
Also it requires users to #include <iterator> in order to use the new looping construct. There's precedent for that, though, because users must #include <typeinfo> to use typeid. I can't decide how I feel about that. Perhaps there's another way.
I spoke with several implementers and they all said that we need to include some special header...otherwise it is very problematic to let the compiler and standard library work together.
It surprises me a bit that Thorsten makes no mention of BOOST_FOREACH in this proposal, though. Seems relevant, if only to establish interest and existing practice.
yeah, sorry about that. I think I actually had some of your stuff in there, but people where confused about what I was actually trying to propose...so I cut some stuff away. Anyway, I should mention your work...and I will when I get a change to present it in Quebec or later. best regards -Thorsten