fix issue 3891

modules/core/include/opencv2/core/mat.inl.hpp

@@ -1586,7 +1586,13 @@ template<typename _Tp> template<int n> inline
 Mat_<_Tp>::operator Vec<typename DataType<_Tp>::channel_type, n>() const
 {
     CV_Assert(n % DataType<_Tp>::channels == 0);
+
+#if defined _MSC_VER
+    const Mat* pMat = (const Mat*)this; // workaround for MSVS <= 2012 compiler bugs (but GCC 4.6 dislikes this workaround)
+    return pMat->operator Vec<typename DataType<_Tp>::channel_type, n>();
+#else
     return this->Mat::operator Vec<typename DataType<_Tp>::channel_type, n>();
+#endif
 }
 
 template<typename _Tp> template<int m, int n> inline
@@ -1594,8 +1600,14 @@ Mat_<_Tp>::operator Matx<typename DataType<_Tp>::channel_type, m, n>() const
 {
     CV_Assert(n % DataType<_Tp>::channels == 0);
 
+#if defined _MSC_VER
+    const Mat* pMat = (const Mat*)this; // workaround for MSVS <= 2012 compiler bugs (but GCC 4.6 dislikes this workaround)
+    Matx<typename DataType<_Tp>::channel_type, m, n> res = pMat->operator Matx<typename DataType<_Tp>::channel_type, m, n>();
+    return res;
+#else
     Matx<typename DataType<_Tp>::channel_type, m, n> res = this->Mat::operator Matx<typename DataType<_Tp>::channel_type, m, n>();
     return res;
+#endif
 }
 
 template<typename _Tp> inline

modules/core/test/test_mat.cpp

@@ -1214,7 +1214,7 @@ TEST(Core_Matx, fromMat_)
 {
     Mat_<double> a = (Mat_<double>(2,2) << 10, 11, 12, 13);
     Matx22d b(a);
-    ASSERT_EQ( norm(a, b, NORM_INF), 0.);
+    ASSERT_EQ( cvtest::norm(a, b, NORM_INF), 0.);
 }
 
 TEST(Core_InputArray, empty)