[eigen] Using C++11 features

[Brad Bell <bradbell@xxxxxxxxxx>]

I have found that C++11 features are only partially implemented (on many 
compilers). Hence, I use CMake to detect if a particular C++11 feature 
is available, and if so use it. For example, see
https://projects.coin-or.org/CppAD/browser/trunk/cppad/CMakeLists.txt
where the following code checks for the C++11 null_ptr feature:

# 
-----------------------------------------------------------------------------
# cppad_has_nullptr
#
# CHECK_CXX_SOURCE_RUNS(source variable)
SET(CMAKE_REQUIRED_INCLUDES  "")
SET(CMAKE_REQUIRED_LIBRARIES "")
SET(CMAKE_REQUIRED_FLAGS     ${cppad_cxx_flags})
SET(source "
int main(void)
{    char *c = nullptr;
     return 0;
}" )
CHECK_CXX_SOURCE_RUNS("${source}" nullptr_ok)
IF( nullptr_ok )
     SET(cppad_has_nullptr 1)
ELSE( nullptr_ok )
     SET(cppad_has_nullptr 0)
ENDIF( nullptr_ok )
MESSAGE(STATUS "cppad_has_nullptr = ${cppad_has_nullptr}" )



On 10/30/2013 3:17 PM, Christoph Hertzberg wrote:
> On 30.10.2013 20:02, Jim Garrison wrote:
> > On 10/30/2013 03:20 AM, Christoph Hertzberg wrote:
> > > Generally, I agree that we should use more C++11 features in the 
> > > future.
> > > It does however bear the risk that projects using those features
> > > immediately lose compatibility to older compilers (which unfortunately
> > > are still common e.g. for embedded systems) -- that's especially the
> > > case if we introduce new core functionality depending on C++11.
> >
> > Actually, this is one of the reasons I suggested using a #define to
> > enable Eigen's C++11 features.  If one must manually define
> > EIGEN_ENABLE_CXX11, it will remove the risk that a project begins using
> > C++11 features without realizing it.
>
> Yes, that's actually a good point. There were some points, where we 
> need to detect C++11 to circumvent incompatibilities (something about 
> allocators, IIRC).
> So maybe an only user-defined EIGEN_ENABLE_CXX11 and an auto-detected 
> EIGEN_HAS_CXX11.
>
> > Another issue is that some compiler versions claim to support C++11
> > through their __cplusplus macro, but do not support all C++11 features.
>
> Yes, I'm afraid that some problems will appear, once more people start 
> experimenting with C++11 and with more exotic compilers (AFAIK, no 
> major compiler has it enabled by default as of now?)
>
>
> BTW: Please just answer to the list, I'm getting every mail twice ...
>
> Christoph