[c++11] add support for C++11 constexpr

As decided on the developer meeting in Aachen, we support (but do not
rely on) the C++11 keyword constexpr. This patch adds an m4-check for
constexpr and a header (cxx11.hh) defining a macro DUNE_CONSTEXPR either
as constexpr or empty (depending on the compiler support for it). It is
then used in FieldVector and FieldMatrix on size, rows, and cols.

dune/common/CMakeLists.txt

@@ -31,6 +31,7 @@ install(FILES
         bitsetvector.hh
         classname.hh
         collectivecommunication.hh
+        cxx11.hh
         debugallocator.hh
         debugstream.hh
         deprecated.hh

dune/common/Makefile.am

@@ -28,6 +28,7 @@ commoninclude_HEADERS = 			\
 	bitsetvector.hh				\
 	classname.hh				\
 	collectivecommunication.hh		\
+	cxx11.hh				\
 	debugallocator.hh			\
 	debugstream.hh				\
 	deprecated.hh				\

dune/common/cxx11.hh

+#ifndef DUNE_COMMON_CXX11_HH
+#define DUNE_COMMON_CXX11_HH
+
+#if HAVE_CONSTEXPR
+#define DUNE_CONSTEXPR constexpr
+#else // #if HAVE_CONSTEXPR
+#define DUNE_CONSTEXPR
+#endif // #else // #if HAVE_CONSTEXPR
+
+#endif // #ifndef DUNE_COMMON_CXX11_HH

dune/common/fmatrix.hh

@@ -8,6 +8,7 @@
 #include <cstddef>
 #include <iostream>
 
+#include <dune/common/cxx11.hh>
 #include <dune/common/exceptions.hh>
 #include <dune/common/fvector.hh>
 #include <dune/common/densematrix.hh>
@@ -168,8 +169,8 @@ namespace Dune
     }
 
     // make this thing a matrix
-    size_type mat_rows() const { return ROWS; }
-    size_type mat_cols() const { return COLS; }
+    DUNE_CONSTEXPR size_type mat_rows() const { return ROWS; }
+    DUNE_CONSTEXPR size_type mat_cols() const { return COLS; }
 
     row_reference mat_access ( size_type i )
     {
@@ -270,8 +271,8 @@ namespace Dune
     }
 
     // make this thing a matrix
-    size_type mat_rows() const { return 1; }
-    size_type mat_cols() const { return 1; }
+    DUNE_CONSTEXPR size_type mat_rows() const { return 1; }
+    DUNE_CONSTEXPR size_type mat_cols() const { return 1; }
 
     row_reference mat_access ( size_type i )
     {

dune/common/fvector.hh

@@ -11,6 +11,8 @@
 #include <cstring>
 #include <utility>
 
+#include <dune/common/cxx11.hh>
+
 #include "typetraits.hh"
 #include "exceptions.hh"
 #include "array.hh"
@@ -156,8 +158,10 @@ namespace Dune {
     }
     using Base::operator=;
 
+    DUNE_CONSTEXPR size_type size () const { return vec_size(); }
+
     // make this thing a vector
-    size_type vec_size() const { return SIZE; }
+    DUNE_CONSTEXPR size_type vec_size () const { return SIZE; }
     K & vec_access(size_type i) { return _data[i]; }
     const K & vec_access(size_type i) const { return _data[i]; }
   private:
@@ -243,8 +247,10 @@ namespace Dune {
       return *this;
     }
 
+    DUNE_CONSTEXPR size_type size () const { return vec_size(); }
+
     //===== forward methods to container
-    size_type vec_size() const { return 1; }
+    DUNE_CONSTEXPR size_type vec_size () const { return 1; }
     K & vec_access(size_type i)
     {
       assert(i == 0);

m4/cxx11_constexpr.m4

+# tests for C++11 constexpr support
+# the associated macro is called HAVE_CONSTEXPR
+
+AC_DEFUN([CXX11_CONSTEXPR_CHECK],[
+  AC_CACHE_CHECK([for C++11 constexpr], dune_cv_cxx11_constexpr_support, [
+    AC_REQUIRE([AC_PROG_CXX])
+    AC_REQUIRE([GXX0X])
+    AC_LANG_PUSH([C++])
+    AC_COMPILE_IFELSE([
+      AC_LANG_PROGRAM([
+          constexpr int foo () { return 0; }
+
+          template< int v >
+          struct A
+          {
+            static const int value = v;
+          };
+        ],[
+          return A< foo() >::value;
+        ])],
+      dune_cv_cxx11_constexpr_support=yes,
+      dune_cv_cxx11_constexpr_support=no)
+    AC_LANG_POP
+  ])
+  if test "x$dune_cv_cxx11_constexpr_support" = xyes; then
+    AC_DEFINE(HAVE_CONSTEXPR, 1, [Define to 1 if C++11 constexpr is supported])
+  fi
+])

m4/dune_common.m4

@@ -26,6 +26,7 @@ AC_DEFUN([DUNE_COMMON_CHECKS],
   AC_REQUIRE([RVALUE_REFERENCES_CHECK])
   AC_REQUIRE([INITIALIZER_LIST_CHECK])
   AC_REQUIRE([CXX11_CONDITIONAL_CHECK])
+  AC_REQUIRE([CXX11_CONSTEXPR_CHECK])
   AC_REQUIRE([DUNE_BOOST_BASE])
   AC_REQUIRE([MAKE_SHARED])
   AC_REQUIRE([DUNE_LINKCXX])