Clarify error message when writing to a read-only sparse-sub-matrix.

Eigen/src/SparseCore/SparseBlock.h

@@ -73,8 +73,15 @@ public:
     Index m_outerStart;
     const internal::variable_if_dynamic<Index, OuterSize> m_outerSize;
   
-  public:
+  protected:
-    EIGEN_INHERIT_ASSIGNMENT_OPERATORS(BlockImpl)
+    // Disable assignment with clear error message.
+    // Note that simply removing operator= yields compilation errors with ICC+MSVC
+    template<typename T>
+    BlockImpl& operator=(const T&)
+    {
+      EIGEN_STATIC_ASSERT(sizeof(T)==0, THIS_SPARSE_BLOCK_SUBEXPRESSION_IS_READ_ONLY);
+      return *this;
+    }
 };
 
 
@@ -425,14 +432,22 @@ public:
     
     Index nonZeros() const { return Dynamic; }
 
-    EIGEN_INHERIT_ASSIGNMENT_OPERATORS(BlockImpl)
-
     typename internal::ref_selector<XprType>::non_const_type m_matrix;
     const internal::variable_if_dynamic<Index, XprType::RowsAtCompileTime == 1 ? 0 : Dynamic> m_startRow;
     const internal::variable_if_dynamic<Index, XprType::ColsAtCompileTime == 1 ? 0 : Dynamic> m_startCol;
     const internal::variable_if_dynamic<Index, RowsAtCompileTime> m_blockRows;
     const internal::variable_if_dynamic<Index, ColsAtCompileTime> m_blockCols;
 
+  protected:
+    // Disable assignment with clear error message.
+    // Note that simply removing operator= yields compilation errors with ICC+MSVC
+    template<typename T>
+    BlockImpl& operator=(const T&)
+    {
+      EIGEN_STATIC_ASSERT(sizeof(T)==0, THIS_SPARSE_BLOCK_SUBEXPRESSION_IS_READ_ONLY);
+      return *this;
+    }
+
 };
 
 namespace internal {