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unsupported/ C++11 workarounds: don't use hack for libc++ if not required

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libc++ from 3.4 onwards supports constexpr std::get, but only if
compiled with -std=c++1y. Change the detection so that libc++'s
internals are only used if either -std=c++1y is not specified or the
library is too old, making the whole hack a bit more future-proof.
This commit is contained in:
Christian Seiler 2014-06-04 18:47:42 +02:00
parent 45515779d3
commit 58cfac9a12
1 changed files with 4 additions and 2 deletions
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6
unsupported/Eigen/CXX11/src/Core/util/CXX11Workarounds.h
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@ -48,13 +48,15 @@ namespace internal {
* - libstdc++ from version 4.7 onwards has it nevertheless,
* so use that
* - libstdc++ older versions: use _M_instance directly
* - libc++ all versions so far: use __elems_ directly
* - libc++ from version 3.4 onwards has it IF compiled with
* -std=c++1y
* - libc++ older versions or -std=c++11: use __elems_ directly
* - all other libs: use std::get to be portable, but
* this may not be constexpr
*/
#if defined(__GLIBCXX__) && __GLIBCXX__ < 20120322
#define STD_GET_ARR_HACK a._M_instance[I]
#elif defined(_LIBCPP_VERSION)
#elif defined(_LIBCPP_VERSION) && (!defined(_LIBCPP_STD_VER) || _LIBCPP_STD_VER <= 11)
#define STD_GET_ARR_HACK a.__elems_[I]
#else
#define STD_GET_ARR_HACK std::template get<I, T, N>(a)