Compile time detection for unimplemented stl-style iterators

1 files changed, 13 insertions, 0 deletions

diff --git a/Eigen/src/Core/StlIterators.h b/Eigen/src/Core/StlIterators.h
index 24eef1269..5f2edc4e6 100644
--- a/Eigen/src/Core/StlIterators.h
+++ b/Eigen/src/Core/StlIterators.h
@@ -11,6 +11,19 @@ namespace Eigen {
 
 namespace internal {
 
+// Iterator type for XprType that do not support stl-style iterators. Allows to
+// detect that expression does not support stl iterators at compile time.
+template<typename XprType>
+class not_an_iterator
+{
+  not_an_iterator() : mp_xpr(0), m_index(0) {}
+  not_an_iterator(XprType& xpr, Index index) : mp_xpr(&xpr), m_index(index) {}
+
+ protected:
+  XprType *mp_xpr;
+  Index m_index;
+};
+
 template<typename XprType,typename Derived>
 class indexed_based_stl_iterator_base
 {