Sincerely,
Whit
On Mon, Oct 7, 2013 at 5:47 PM, Dirk Eddelbuettel <edd at debian.org>
wrote:
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-bounces at r-project.org
[r-devel-bounces at r-project.org] on
behalf of Dirk Eddelbuettel [edd at 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 at 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 at 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 | edd at debian.org | http://dirk.eddelbuettel.com
|
| ______________________________________________
| R-devel at r-project.org mailing list
| https://stat.ethz.ch/mailman/listinfo/r-devel
|
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Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com