From 847f72f38eb4809e61233872f375b1e4c183de13 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Steffen=20M=C3=BCthing?= <muething@dune-project.org>
Date: Tue, 10 Mar 2015 19:51:41 +0100
Subject: [PATCH] [Typetraits][Compatibility] Provide partial backwards
compatibility for is_indexable on old GCC versions
Older GCC versions have some nasty bugs related to SFINAE and indexing
with operator[]. This patch adds a configuration check for those
problems and a partial backwards compatibility hack for those older
compilers that is sufficient for our current use case in the VTK
writer.
---
cmake/modules/CheckCXX11Features.cmake | 49 +++++++++++
config.h.cmake | 3 +
dune/common/typetraits.hh | 111 +++++++++++++++++++++++--
m4/CMakeLists.txt | 1 +
m4/Makefile.am | 1 +
m4/cxx11_is_indexable_support.m4 | 64 ++++++++++++++
m4/dune_common.m4 | 3 +-
7 files changed, 226 insertions(+), 6 deletions(-)
create mode 100644 m4/cxx11_is_indexable_support.m4
diff --git a/cmake/modules/CheckCXX11Features.cmake b/cmake/modules/CheckCXX11Features.cmake
index 611cacf72..85ad3689d 100644
--- a/cmake/modules/CheckCXX11Features.cmake
+++ b/cmake/modules/CheckCXX11Features.cmake
@@ -217,6 +217,55 @@ check_cxx_source_compiles("
" HAVE_STD_DECLVAL
)
+# full support for is_indexable (checking whether a type supports operator[])
+check_cxx_source_compiles("
+ #include <utility>
+ #include <type_traits>
+ #include <array>
+
+ template <class T>
+ typename std::add_rvalue_reference<T>::type declval();
+
+ namespace detail {
+
+ template<typename T, typename I, typename = int>
+ struct _is_indexable
+ : public std::false_type
+ {};
+
+ template<typename T, typename I>
+ struct _is_indexable<T,I,typename std::enable_if<(sizeof(declval<T>()[declval<I>()]) > 0),int>::type>
+ : public std::true_type
+ {};
+
+ }
+
+ template<typename T, typename I = std::size_t>
+ struct is_indexable
+ : public detail::_is_indexable<T,I>
+ {};
+
+ struct foo_type {};
+
+ int main()
+ {
+ double x;
+ std::array<double,4> y;
+ double z[5];
+ foo_type f;
+
+ static_assert(not is_indexable<decltype(x)>::value,\"scalar type\");
+ static_assert(is_indexable<decltype(y)>::value,\"indexable class\");
+ static_assert(is_indexable<decltype(z)>::value,\"array\");
+ static_assert(not is_indexable<decltype(f)>::value,\"not indexable class\");
+ static_assert(not is_indexable<decltype(y),foo_type>::value,\"custom index type\");
+
+ return 0;
+ }
+" HAVE_IS_INDEXABLE_SUPPORT
+ )
+
+
cmake_pop_check_state()
# find the threading library
diff --git a/config.h.cmake b/config.h.cmake
index ce6599063..9f6b370c1 100644
--- a/config.h.cmake
+++ b/config.h.cmake
@@ -116,6 +116,9 @@
/* Define to 1 if C++11 std::declval() is supported */
#cmakedefine HAVE_STD_DECLVAL 1
+/* Define to 1 if the compiler properly supports testing for operator[] */
+#cmakedefine HAVE_IS_INDEXABLE_SUPPORT 1
+
/* does the compiler support the keyword 'final'? */
#cmakedefine HAVE_KEYWORD_FINAL 1
diff --git a/dune/common/typetraits.hh b/dune/common/typetraits.hh
index 64f745c6e..933a43797 100644
--- a/dune/common/typetraits.hh
+++ b/dune/common/typetraits.hh
@@ -6,6 +6,7 @@
#include <type_traits>
#include <dune/common/deprecated.hh>
+#include <dune/common/std/utility.hh>
namespace Dune
{
@@ -404,23 +405,123 @@ namespace Dune
static const bool value = true;
};
- namespace {
- template<typename T, typename I, decltype(*(static_cast<T*>(nullptr))[*(static_cast<T*>(nullptr))],0) = 0>
- auto _is_indexable(T*) -> std::true_type;
+#if defined(DOXYGEN) or HAVE_IS_INDEXABLE_SUPPORT
+
+#ifndef DOXYGEN
+
+ namespace detail {
+
+ template<typename T, typename I, typename = int>
+ struct _is_indexable
+ : public std::false_type
+ {};
template<typename T, typename I>
- auto _is_indexable(void*) -> std::false_type;
+ struct _is_indexable<T,I,typename std::enable_if<(sizeof(Std::declval<T>()[Std::declval<I>()]) > 0),int>::type>
+ : public std::true_type
+ {};
}
+#endif // DOXYGEN
+
//! Type trait to determine whether an instance of T has an operator[](I), i.e. whether
//! it can be indexed with an index of type I.
+ /**
+ * \warning Not all compilers support testing for arbitrary index types. In particular, there
+ * are problems with GCC 4.4 and 4.5.
+ */
template<typename T, typename I = std::size_t>
struct is_indexable
- : public decltype(_is_indexable<T,I>(static_cast<T*>(nullptr)))
+ : public detail::_is_indexable<T,I>
{};
+
+#else // defined(DOXYGEN) or HAVE_IS_INDEXABLE_SUPPORT
+
+
+ // okay, here follows a mess of compiler bug workarounds...
+ // GCC 4.4 dies if we try to subscript a simple type like int and
+ // both GCC 4.4 and 4.5 don't like using arbitrary types as subscripts
+ // for macros.
+ // So we make sure to only ever attempt the SFINAE for operator[] for
+ // class types, and to make sure the compiler doesn't become overly eager
+ // we have to do some lazy evaluation tricks with nested templates and
+ // stuff.
+ // Let's get rid of GCC 4.4 ASAP!
+
+
+ namespace detail {
+
+ // simple wrapper template to support the lazy evaluation required
+ // in _is_indexable
+ template<typename T>
+ struct _lazy
+ {
+ template<typename U>
+ struct evaluate
+ {
+ typedef T type;
+ };
+ };
+
+ // default version, gets picked if SFINAE fails
+ template<typename T, typename = int>
+ struct _is_indexable
+ : public std::false_type
+ {};
+
+ // version for types supporting the subscript operation
+ template<typename T>
+ struct _is_indexable<T,decltype(Std::declval<T>()[0],0)>
+ : public std::true_type
+ {};
+
+ // helper struct for delaying the evaluation until we are sure
+ // that T is a class (i.e. until we are outside std::conditional
+ // below)
+ struct _check_for_index_operator
+ {
+
+ template<typename T>
+ struct evaluate
+ : public _is_indexable<T>
+ {};
+
+ };
+
+ }
+
+ // The rationale here is as follows:
+ // 1) If we have an array, we assume we can index into it. That isn't
+ // true if I isn't an integral type, but that's why we have the static assertion
+ // in the body - we could of course try and check whether I is integral, but I
+ // can't be arsed and want to provide a motivation to switch to a newer compiler...
+ // 2) If we have a class, we use SFINAE to check for operator[]
+ // 3) Otherwise, we assume that T does not support indexing
+ //
+ // In order to make sure that the compiler doesn't accidentally try the SFINAE evaluation
+ // on an array or a scalar, we have to resort to lazy evaluation.
+ template<typename T, typename I = std::size_t>
+ struct is_indexable
+ : public std::conditional<
+ std::is_array<T>::value,
+ detail::_lazy<std::true_type>,
+ typename std::conditional<
+ std::is_class<T>::value,
+ detail::_check_for_index_operator,
+ detail::_lazy<std::false_type>
+ >::type
+ >::type::template evaluate<T>::type
+ {
+ static_assert(std::is_same<I,std::size_t>::value,"Your compiler is broken and does not support checking for arbitrary index types");
+ };
+
+
+#endif // defined(DOXYGEN) or HAVE_IS_INDEXABLE_SUPPORT
+
+
/** @} */
}
#endif
diff --git a/m4/CMakeLists.txt b/m4/CMakeLists.txt
index e91561816..749751f13 100644
--- a/m4/CMakeLists.txt
+++ b/m4/CMakeLists.txt
@@ -8,6 +8,7 @@ install(PROGRAMS
ax_lang_compiler_ms.m4
boost_fusion.m4
cxx11_compiler.m4
+ cxx11_is_indexable_support.m4
cxx0x_nullptr.m4
cxx11_constexpr.m4
cxx11_final.m4
diff --git a/m4/Makefile.am b/m4/Makefile.am
index a2f87b8d3..ea8865717 100644
--- a/m4/Makefile.am
+++ b/m4/Makefile.am
@@ -14,6 +14,7 @@ ALLM4S = \
cxx0x_nullptr.m4 \
cxx11_constexpr.m4 \
cxx11_final.m4 \
+ cxx11_is_indexable_support.m4 \
cxx11_noexcept.m4 \
cxx11_range_based_for.m4 \
cxx11_std_declval.m4 \
diff --git a/m4/cxx11_is_indexable_support.m4 b/m4/cxx11_is_indexable_support.m4
new file mode 100644
index 000000000..ff5aba8f0
--- /dev/null
+++ b/m4/cxx11_is_indexable_support.m4
@@ -0,0 +1,64 @@
+# tests whether the compiler properly supports testing for operator[]
+# the associated macro is called HAVE_IS_INDEXABLE_SUPPORT
+
+AC_DEFUN([DUNE_CXX11_IS_INDEXABLE_SUPPORT_CHECK],[
+ AC_CACHE_CHECK([whether the compiler properly supports testing for operator[[]]],
+ dune_cv_cxx11_is_indexable_support,
+ [
+ AC_REQUIRE([AC_PROG_CXX])
+ AC_REQUIRE([CXX11])
+ AC_LANG_PUSH([C++])
+ AC_COMPILE_IFELSE([
+ AC_LANG_PROGRAM(
+ [
+ #include <utility>
+ #include <type_traits>
+ #include <array>
+
+ template <class T>
+ typename std::add_rvalue_reference<T>::type declval();
+
+ namespace detail {
+
+ template<typename T, typename I, typename = int>
+ struct _is_indexable
+ : public std::false_type
+ {};
+
+ template<typename T, typename I>
+ struct _is_indexable<T,I,typename std::enable_if<(sizeof(declval<T>()[[declval<I>()]]) > 0),int>::type>
+ : public std::true_type
+ {};
+
+ }
+
+ template<typename T, typename I = std::size_t>
+ struct is_indexable
+ : public detail::_is_indexable<T,I>
+ {};
+
+ struct foo_type {};
+
+ ],[
+ double x;
+ std::array<double,4> y;
+ double z[[5]];
+ foo_type f;
+
+ static_assert(not is_indexable<decltype(x)>::value,"scalar type");
+ static_assert(is_indexable<decltype(y)>::value,"indexable class");
+ static_assert(is_indexable<decltype(z)>::value,"array");
+ static_assert(not is_indexable<decltype(f)>::value,"not indexable class");
+ static_assert(not is_indexable<decltype(y),foo_type>::value,"custom index type");
+
+ return 0;
+ ])],
+ dune_cv_cxx11_is_indexable_support=yes,
+ dune_cv_cxx11_is_indexable_support=no)
+ AC_LANG_POP
+ ])
+ if test "$dune_cv_cxx11_is_indexable_support" = yes; then
+ AC_DEFINE(HAVE_IS_INDEXABLE_SUPPORT, 1,
+ [Define to 1 if the compiler properly supports testing for operator[[]]])
+ fi
+])
diff --git a/m4/dune_common.m4 b/m4/dune_common.m4
index a065f2e2c..9dcf65e6e 100644
--- a/m4/dune_common.m4
+++ b/m4/dune_common.m4
@@ -28,6 +28,7 @@ AC_DEFUN([DUNE_COMMON_CHECKS],
AC_REQUIRE([DUNE_CHECKFINAL])
AC_REQUIRE([DUNE_CHECKUNUSED])
AC_REQUIRE([DUNE_CXX11_STD_DECLVAL_CHECK])
+ AC_REQUIRE([DUNE_CXX11_IS_INDEXABLE_SUPPORT_CHECK])
AC_REQUIRE([DUNE_CHECK_CXA_DEMANGLE])
AC_REQUIRE([DUNE_SET_MINIMAL_DEBUG_LEVEL])
AC_REQUIRE([DUNE_PATH_XDR])
@@ -40,7 +41,7 @@ AC_DEFUN([DUNE_COMMON_CHECKS],
])
DUNE_ADD_MODULE_DEPS([dune-common], [STDTHREAD], [${STDTHREAD_CPPFLAGS}],
[${STDTHREAD_LDFLAGS}], [${STDTHREAD_LIBS}])
-
+
dnl check for programs
AC_REQUIRE([AC_PROG_CC])
# add -Wall if the compiler is gcc
--
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