From d953de45029c7196283522c759c45325ebe3636a Mon Sep 17 00:00:00 2001
From: Tobias Malkmus <tomalk@mathematik.uni-freiburg.de>
Date: Thu, 14 Sep 2017 15:57:32 +0200
Subject: [PATCH] [optinal] use std::optional on newer compilers
---
cmake/modules/CheckCXXFeatures.cmake | 18 ++++++++++++++++++
config.h.cmake | 3 +++
dune/common/std/optional.hh | 17 +++++++++++++++++
3 files changed, 38 insertions(+)
diff --git a/cmake/modules/CheckCXXFeatures.cmake b/cmake/modules/CheckCXXFeatures.cmake
index c4075d411..f2c510709 100644
--- a/cmake/modules/CheckCXXFeatures.cmake
+++ b/cmake/modules/CheckCXXFeatures.cmake
@@ -22,6 +22,9 @@
# :code:`DUNE_HAVE_CXX_CLASS_TEMPLATE_ARGUMENT_DEDUCTION`
# True if C++17's class template argument deduction is supported
#
+# :code:`DUNE_HAVE_CXX_OPTIONAL`
+# True if C++17's optional implementation is supported
+#
# .. cmake_variable:: DISABLE_CXX_VERSION_CHECK
#
# You may set this variable to TRUE to disable checking for
@@ -350,6 +353,21 @@ check_cxx_source_compiles("
" DUNE_HAVE_CXX_CLASS_TEMPLATE_ARGUMENT_DEDUCTION
)
+
+# support for C++17's optional implementation
+check_cxx_source_compiles("
+ #include <optional>
+ #include <string>
+
+ int main()
+ {
+ std::optional< std::string > a;
+ std::string b = a.value_or( \"empty\" );
+ }
+" DUNE_HAVE_CXX_OPTIONAL
+ )
+
+
# find the threading library
# Use a copy FindThreads from CMake 3.1 due to its support of pthread
if(NOT DEFINED THREADS_PREFER_PTHREAD_FLAG)
diff --git a/config.h.cmake b/config.h.cmake
index 1af815551..e06c65b73 100644
--- a/config.h.cmake
+++ b/config.h.cmake
@@ -29,6 +29,9 @@
/* does the compiler support C++17's class template argument deduction? */
#cmakedefine DUNE_HAVE_CXX_CLASS_TEMPLATE_ARGUMENT_DEDUCTION 1
+/* does the compiler support C++17's optional? */
+#cmakedefine DUNE_HAVE_CXX_OPTIONAL 1
+
/* does the compiler support conditionally throwing exceptions in constexpr context? */
#cmakedefine DUNE_SUPPORTS_CXX_THROW_IN_CONSTEXPR 1
diff --git a/dune/common/std/optional.hh b/dune/common/std/optional.hh
index 55807184e..f31aabb6c 100644
--- a/dune/common/std/optional.hh
+++ b/dune/common/std/optional.hh
@@ -7,12 +7,24 @@
#include <type_traits>
#include <utility>
+#ifdef DUNE_HAVE_CXX_OPTIONAL
+#include <optional>
+#endif // #ifdef DUNE_HAVE_CXX_OPTIONAL
+
+
namespace Dune
{
namespace Std
{
+#ifdef DUNE_HAVE_CXX_OPTIONAL
+ // In case of C++ standard >= 17 we forward optionals into our namespace
+ template< class T >
+ using optional = std::optional< T >;
+#else
+ // In case of C++ standard < 17 we take the fallback implementation
+
// nullopt
// -------
@@ -414,11 +426,14 @@ namespace Dune
return optional< typename std::decay< T >::type >( std::forward< T >( value ) );
}
+#endif //#ifdef DUNE_HAVE_CXX_OPTIONAL
+
} // namespace Std
} // namespace Dune
+#ifndef DUNE_HAVE_CXX_OPTIONAL
namespace std
{
@@ -447,4 +462,6 @@ namespace std
} // namespace std
+#endif //#ifndef DUNE_HAVE_CXX_OPTIONAL
+
#endif // #ifndef DUNE_COMMON_STD_OPTIONAL_HH
--
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