started a better implementation the static assertions

[[Imported from SVN: r5039]]

common/static_assert.hh

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+#ifndef DUNE_STATIC_ASSERT_HH
+#define DUNE_STATIC_ASSERT_HH
+
+/**
+    \brief Helper template so that compilation fails if condition is not true.
+
+    If the condition is true a static function yes is available, othewise the
+    only function available is no().
+
+    Example for compile time check whether two types are the same:
+    \code
+    IsTrue<is_same<int,int>::value>::yes(); //
+    IsTrue<is_same<bool,int>::value>::yes(); // false, will trigger a compile time error
+    \endcode
+
+    A test that trigger a compile time error if condition is true:
+    \code
+    IsTrue<condition>::no()
+    \endcode
+ */
+template <bool condition>
+struct IsTrue
+{
+  static void no() {};
+};
+
+template <>
+struct IsTrue<true>
+{
+  static void yes() {};
+};
+
+
+#include <iostream>
+
+// Taken from BOOST
+//
+// Helper macro CPPMAGIC_JOIN:
+// The following piece of macro magic joins the two
+// arguments together, even when one of the arguments is
+// itself a macro (see 16.3.1 in C++ standard).  The key
+// is that macro expansion of macro arguments does not
+// occur in CPPMAGIC_DO_JOIN2 but does in CPPMAGIC_DO_JOIN.
+//
+#define CPPMAGIC_JOIN( X, Y ) CPPMAGIC_DO_JOIN( X, Y )
+#define CPPMAGIC_DO_JOIN( X, Y ) CPPMAGIC_DO_JOIN2(X,Y)
+#define CPPMAGIC_DO_JOIN2( X, Y ) X ## Y
+
+template <bool x> struct static_assert_failure;
+
+template <> struct static_assert_failure<true> { };
+
+template<int x> struct static_assert_test {};
+
+/**
+   dune_static_assert(1<=2, "fehler");
+   dune_static_assert(1<=3, "fehler");
+   dune_static_assert(3<=2, "fehler");
+ */
+#define dune_static_assert(B,MSG) \
+  typedef static_assert_test<\
+    sizeof(static_assert_failure< (bool)( B )>)\
+    > CPPMAGIC_JOIN (dune_static_assert_typedef_, __LINE__)
+
+#endif