Move range exception outside of the bound checking macro

Somehow, this seems to work in contexpr cases. Previous code always failed due some instantiation of Dune::RangeError

dune/common/boundschecking.hh

@@ -19,6 +19,14 @@
 #ifndef DUNE_ASSERT_BOUNDS
 #if defined(DUNE_CHECK_BOUNDS) || defined(DOXYGEN)
 
+namespace Dune::Impl
+{
+  void boundCheckThrow()
+  {
+    DUNE_THROW(Dune::RangeError, "Index out of bounds.");
+  }
+}
+
 /**
  * \brief If `DUNE_CHECK_BOUNDS` is defined: check if condition
  * \a cond holds; otherwise, do nothing.
@@ -30,7 +38,7 @@
 #define DUNE_ASSERT_BOUNDS(cond)                            \
   do {                                                      \
     if (!(cond))                                            \
-      DUNE_THROW(Dune::RangeError, "Index out of bounds."); \
+      Dune::Impl::boundCheckThrow();                        \
   } while (false)
 
 #else

dune/common/test/boundscheckingtest.cc

@@ -8,9 +8,25 @@
 #include <dune/common/fvector.hh>
 #include <dune/common/fmatrix.hh>
 
+// simple bound checking in a constant evaluated context
+constexpr bool constexprCheck(std::size_t i, bool do_check) {
+  if (do_check)
+    DUNE_ASSERT_BOUNDS(i==0);
+  return i==0;
+}
+
 int main() try {
   bool passed = true;
 
+  // check that throw branch does not get evaluated
+  static_assert(constexprCheck(0, true));
+
+  // check that assert branch does not get evaluated
+  static_assert(!constexprCheck(1, false));
+
+  // this (rightfuly) fails to compile due a exception path not being constexpr
+  // static_assert(constexprCheck(1, true));
+
   // Write beyond end of singleton vector
   try {
     Dune::FieldVector<double, 1> v = {1};