On Wed, Feb 2, 2011 at 1:46 PM, Bryce Lelbach <admin@thefireflyproject.us> wrote:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
I believe I've got the de-facto role of clang (linux) maintainer. Clang-linux C++0x support is very shaky (turning it on can break stdlib stuff) unless you have a clang compiled GNU stdlib or libc++. Until Redhat-based and Debian- based distros start shipping Clang with either 0.) clang-compiled GNU stdlib or 1.) clang friendly stdlib, we should probably only try to use C++0x support on Darwin. I need to investigate this more, though.
There are a number of inter-related issues here, so let me try to detangle them. Clang itself is just now getting some C++0x support. It has rvalue references, variadic templates, decltype, static_assert, and some other goodies. We think it's in decent shape, but obviously we need more testing coverage. Clang works with a few different C++ standard libraries, and that's where C++0x gets interesting/messy: - libc++ (Clang/LLVM's new C++0x standard library) works great with Clang's C++0x support. - libstdc++ (GCC's C++ standard library) has problems with Clang's C++0x support, for different reasons in different versions: 4.2: "works", because it doesn't use any C++0x features, but of course you don't have any library support libs 4.3, 4.4: fails, because the library was written at a time when rvalue references could bind to lvalues, which they now can't. so, Clang C++0x (correctly) rejects the code. This is just a casualty of shipping compilers and libraries based on an incomplete working paper. 4.5: fails, because the library uses generalized initializer lists, which Clang does not yet implement. 4.6: presumably fails because of both generalized initializer lists and constexpr, neither of which Clang does not yet implement. So, at this point, it only really makes sense to test Clang's C++0x support either with libstdc++'s 4.2's non-C++0x library or with libc++. (I haven't tried Dinkumware or Apache; I suspect they'll need to be taught about Clang first).
Hopefully there's a way to turn on C++0x support for clang by defining a macro, without making the stdlib believe that clang supports C++0x.
I don't think this is going to be practical. For libstdc++, we'll probably have to write off 4.3 and 4.4 as great experiments with C++0x that shouldn't be used for writing actual C++0x code, and we'll have to wait until Clang's C++0x support catches up with GCC used of C++0x in the library for 4.5/4.6. Regarding Beman's original question about <boost/config/compiler/clang.hpp>, I'll be happy to keep it up-to-date with feature checks for Clang, since I'm also the maintainer of the feature checks on the Clang side. I'm not a good candidate for platform champion, though, because I don't watch Boost closely enough to be helpful. - Doug