[Rd] CXX_STD and configure.ac in packages

[Martyn Plummer]

On Mon, 2014-03-31 at 07:09 +0000, Martyn Plummer wrote:
> Hi Martin,
> 
> Thanks for the patch. I have applied it. I also added CXX1X and friends to the list of approved variables for R CMD config.
> So you can now query the existence of C++11 support with `R CMD config CXX1X` (It is empty if C++11 support is not available)
> and then take appropriate action in your configure script if, in Dirk's words, you want to do the configure dance.
> 
> The philosophy underlying C++ support in R is that there are only two standards - C++98 and C++11 - and that
> you should write to one of those standards. 

A should add a clarification. The way I wrote this makes it sound like
an even-handed choice, but only C++98 has cross-platform support. If you
use C++11 then many users will not currently be able to use your code. 

> Nobody should be writing new code that uses TR1 extensions now: they are
> superseded by the new standard.
> 
> The map and unordered_map classes are a corner case, as they offer the same functionality but latter has much better
> complexity guarantees, so it is tempting to use it when available.  But from a global perspective you should think of
> C++98 and C++11 as two different languages.
> 
> Martyn
> 
> 
> ________________________________________
> From: r-devel-bounces at r-project.org [r-devel-bounces at r-project.org] on behalf of Romain Francois [romain at r-enthusiasts.com]
> Sent: 31 March 2014 08:22
> To: Martin Morgan
> Cc: R-devel
> Subject: Re: [Rd] CXX_STD and configure.ac in packages
> 
> Hi,
> 
> My advice would be to use SystemRequirements: C++11
> 
> As <unordered_map> is definitely a part of C++11, assuming this version of the standard gives it to you. Your package may not compile on platforms where a C++11 compiler is not available, but perhaps if this becomes a pattern, then such compilers will start to be available, as in the current version of OSX and recent enough versions of various linux distributions.
> 
> The subset of feature that the version of gcc gives you with Rtools might be enough.
> 
> Alternatively, if you use Rcpp, you can use the RCPP_UNORDERED_MAP macro which will expand to either unordered_map or tr1::unordered_map, all the condition compiling is done in Rcpp.
> 
> Romain
> 
> Le 30 mars 2014 à 21:50, Martin Morgan <mtmorgan at fhcrc.org> a écrit :
> 
> > In C++ code for use in a R-3.1.0 package, my specific problem is that I would like to use <unordered_map> if it is available, or <tr1/unordered_map> if not, or <map> if all else fails.
> >
> > I (think I) can accomplish this with configure.ac as
> >
> > AC_INIT("DESCRIPTION")
> >
> > CXX=`"${R_HOME}/bin/R" CMD config CXX`
> > CXXFLAGS=`"${R_HOME}/bin/R" CMD config CXXFLAGS`
> >
> > AC_CONFIG_HEADERS([src/config.h])
> > AC_LANG(C++)
> > AC_CHECK_HEADERS([unordered_map tr1/unordered_map])
> > AC_OUTPUT
> >
> > Use of configure.ac does not seem to be entirely consistent with section 1.2.4 of Writing R Extensions, where one is advised that to use C++(11? see below) code one should
> >
> >    CXX_STD = CXX11
> >
> > in Makevars(.win). My code does not require a compiler that supports the full C++11 feature set. In addition, I do not understand the logic of setting a variable that influences compiler flags in Makevars -- configure.ac will see a compiler with inaccurate flags.
> >
> > Is use of configure.ac orthogonal to setting CXX_STD=CXX11?
> >
> > Some minor typos:
> >
> > /R-3-1-branch$ svn diff
> > Index: doc/manual/R-exts.texi
> > ===================================================================
> > --- doc/manual/R-exts.texi    (revision 65339)
> > +++ doc/manual/R-exts.texi    (working copy)
> > @@ -2250,7 +2250,7 @@
> > @subsection Using C++11 code
> >
> > @R{} can be built without a C++ compiler although one is available
> > -(but not necessarily installed) or all known @R{} platforms.
> > +(but not necessarily installed) on all known @R{} platforms.
> > For full portability across platforms, all
> > that can be assumed is approximate support for the C++98 standard (the
> > widely used @command{g++} deviates considerably from the standard).
> > @@ -2272,7 +2272,7 @@
> > support a flag @option{-std=c++0x}, but the latter only provides partial
> > support for the C++11 standard.
> >
> > -In order to use C++ code in a package, the package's @file{Makevars}
> > +In order to use C++11 code in a package, the package's @file{Makevars}
> > file (or @file{Makevars.win} on Windows) should include the line
> >
> > @example
> > @@ -2329,7 +2329,7 @@
> > anything other than the GNU version of C++98 and GNU extensions (which
> > include TR1).  The default compiler on Windows is GCC 4.6.x and supports
> > the @option{-std=c++0x} flag and some C++11 features (see
> > - at uref{http://gcc.gnu.org/gcc-4.6/cxx0x_status.html}.  On these
> > + at uref{http://gcc.gnu.org/gcc-4.6/cxx0x_status.html}).  On these
> > platforms, it is necessary to select a different compiler for C++11, as
> > described above, @emph{via} personal @file{Makevars} files.  For
> > example, on OS X 10.7 or later one could select @command{clang++}.
> >
> > --
> > Computational Biology / Fred Hutchinson Cancer Research Center
> > 1100 Fairview Ave. N.
> > PO Box 19024 Seattle, WA 98109
> >
> > Location: Arnold Building M1 B861
> > Phone: (206) 667-2793
> >
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> 
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