Hi Martyn, On 7 October 2013 at 21:18, Martyn Plummer wrote: | I don't see any harm in allowing optional C++11 support,
That would be a nice step forward. | and it is no trouble to update the documentation to acknowledge the | existence of C++11 conforming compilers. Indeed. | However, the questions of what is possible, what is recommended, and what | is required for CRAN submissions are distinct. You may be aware of the difficulties we as R package developers have with discussions involving CRAN maintainers. | I have a couple of comments on the macro: | a) Your version implies mandatory C++11 support. One needs | AX_CXX_COMPILE_STDCXX_11(noext,optional) for optional support. I used an existing macros from the GNU autoconf archive. It can certainly be tweaked. R's stack of configure logic is an impressive piece of work and I wasn't expecting this to flow through. It was meant to start a discussion. My principal points are that i) we do have compilers now that can support this, and ii) we can test for their capabilities when R itself is compiled. | b) I find it unhelpful that the macro picks up the partial C++11 support in | gcc 4.7 via the -std=c++0x flag, so I would edit (and rename) the macro to | remove this. Of course. All this can and should be discussed. I just wanted to get the ball rolling and had a choice between just emailing Kurt (as the configure and m4 point man) and emailing here. To the extent that c++0x support is also widely available, I do not see why one could not allow it either. But that is a minor issue: I would really like us to (eventually) move beyond what is going to become a more and more constraining C++ standard. Optional support for deployments where C++11 is indeed available seems like a step in the right direction. Thanks for your feedback! Dirk | Martyn | ________________________________________ | From: r-devel-boun...@r-project.org [r-devel-boun...@r-project.org] on behalf of Dirk Eddelbuettel [e...@debian.org] | Sent: 07 October 2013 01:54 | To: R-devel org | Subject: [Rd] R 3.1.0 and C++11 | | I would like to bring up two issues concerning C++11. | | | First, the R-devel manuals contain incorrect statements regarding C++11: | | i) R-exts.texi: | | Although there is a 2011 version of the C++ standard, it is not yet | fully implemented (nor is it likely to be widely available for some | years) and portable C++ code needs to follow the 1998 standard | (and not use features from C99). | | ii) R-ints.texi: | | The type `R_xlen_t' is made available to packages in C header | `Rinternals.h': this should be fine in C code since C99 is | required. People do try to use R internals in C++, but C++98 | compilers are not required to support these types (and there are | currently no C++11 compilers). | | But since the summer we have g++ and clang with working C++11 implementations: | | iii) g++ implements C++11: | http://isocpp.org/blog/2013/05/gcc-4.8.1-released-c11-feature-complete | | iv) llvm/clang++ implements C++11: | http://isocpp.org/blog/2013/06/llvm-3.3-is-released | | I would suggest to change the wording prior to the release of R 3.1.0 next | year as it is likely that even Microsoft will by then have a fully-conformant | compiler (per Herb Sutter at a recent talk in Chicago). If it helped, I would | be glad to provide minimal patches to the two .texi files. | | Moreover, the C++ Standards Group is working towards closing the delta | between standards being adopted, and compilers being released. They expect | corresponding compilers for C++14 (a "patch" release for C++11 expected to be | ready next spring) to be available within a year---possibly during 2014. | | | Second, the current R Policy regarding C++11 is unnecessarily strict. I would | propose to treat the availability of C++11 extensions more like the | availability of OpenMP: something which configure can probe at build time, | and which can be deployed later via suitable #ifdef tests. | | As a proof of concept, I added this macro from the autoconf archive to the | m4/ directory of R-devel: | | http://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx_11.html | | and made a one-line change to configure.ac (indented two spaces just for email) | | edd@max:~/svn/r-devel$ svn di configure.ac | Index: configure.ac | =================================================================== | --- configure.ac (revision 64031) | +++ configure.ac (working copy) | @@ -906,6 +906,7 @@ | | AC_LANG_PUSH(C++) | AC_OPENMP | +AX_CXX_COMPILE_STDCXX_11(noext) | AC_LANG_POP(C++) | | ### *** ObjC compiler | edd@max:~/svn/r-devel$ | | After running 'aclocal -Im4; autoheader; autoconf', the configure test then | properly detected C++11 (or, in one case, C++0x) on four different compilers: | | [ g++-4.7 case, Ubuntu 13.04 ] | checking whether g++ supports C++11 features by default... no | checking whether g++ supports C++11 features with -std=c++11... no | checking whether g++ supports C++11 features with -std=c++0x... yes | | [ CC=clang CXX=clang++ (3.1), Ubuntu 13.04 ] | checking whether clang++ accepts -M for generating dependencies... yes | checking for clang++ option to support OpenMP... unsupported | checking whether clang++ supports C++11 features by default... no | checking whether clang++ supports C++11 features with -std=c++11... yes | | [ g++-4.8 case, Debian testing ] | checking whether g++ supports C++11 features by default... no | checking whether g++ supports C++11 features with -std=c++11... yes | | [ CC=clang CXX=clang++ (3.2), Debian testing ] | checking whether clang++ supports C++11 features by default... no | checking whether clang++ supports C++11 features with -std=c++11... yes | | It would be easy to another #define to config.h.in. | | | And of course, I understand that R Core is comprised primarily of C | programmers. But to those of us who lean more towards C++ than C, the step | towards C++11 is a big one, and a very exciting one. More and more upstream | authors are considering right now whether to switch to C++11-only. I expect | such switches to become more common as time pass. C++11 provides a lot -- and | preventing programmers from using these tools cannot be in our interest. | | I think that the timing of the next R release will be a good opportunity to | permit use of C++11 where compilers support it -- as a wide range of sites | will already be capable of deploying it. | | Thanks, Dirk | | -- | Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com | | ______________________________________________ | R-devel@r-project.org mailing list | https://stat.ethz.ch/mailman/listinfo/r-devel | ----------------------------------------------------------------------- | This message and its attachments are strictly confidential. 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