revert most of previous commit. It really is better to forbid default

constructor for dynamic-size matrices. Now why do I feel like a beheaded
chicken running around?

Eigen/src/Core/Eval.h

@@ -56,7 +56,6 @@ template<typename Expression> class Eval : NoOperatorEquals,
     typedef Expression Base;
     friend class MatrixBase<Scalar, Expression>;
     
-    Eval() : MatrixType() {}
     Eval(const Expression& expression) : MatrixType(expression) {}
 };
 

Eigen/src/Core/Matrix.h

@@ -163,13 +163,14 @@ class Matrix : public MatrixBase<_Scalar, Matrix<_Scalar, _Rows, _Cols, _Storage
     static Map<Matrix> map(Scalar* array, int size);
     static Map<Matrix> map(Scalar* array);
     
-    /** Default constructor.
+    /** Default constructor, does nothing. Only for fixed-size matrices.
-      *
+      * For dynamic-size matrices and vectors, this constructor is forbidden (guarded by
-      * For fixed-size matrices, does nothing.
+      * an assertion) because it would leave the matrix without an allocated data buffer.
-      *
-      * For dynamic-size matrices, dynamic dimensions are set to 1.
       */
-    explicit Matrix() : Storage() {}
+    explicit Matrix() : Storage()
+    {
+      assert(RowsAtCompileTime > 0 && ColsAtCompileTime > 0);
+    }
     
     /** Constructs a vector or row-vector with given dimension. \only_for_vectors
       *

Eigen/src/Core/MatrixStorage.h

@@ -80,7 +80,7 @@ class MatrixStorage<Scalar, Dynamic, ColsAtCompileTime>
     { return ColsAtCompileTime; }
     
   public:
-    MatrixStorage(int dim = 1) : m_rows(dim)
+    MatrixStorage(int dim) : m_rows(dim)
     {
       m_data = new Scalar[m_rows * ColsAtCompileTime];
     }
@@ -92,6 +92,9 @@ class MatrixStorage<Scalar, Dynamic, ColsAtCompileTime>
     
     ~MatrixStorage()
     { delete[] m_data; }
+    
+  private:
+    MatrixStorage();
 };
 
 template<typename Scalar, int RowsAtCompileTime>
@@ -120,7 +123,7 @@ class MatrixStorage<Scalar, RowsAtCompileTime, Dynamic>
     { return m_cols; }
     
   public:
-    MatrixStorage(int dim = 1) : m_cols(dim)
+    MatrixStorage(int dim) : m_cols(dim)
     {
       m_data = new Scalar[m_cols * RowsAtCompileTime];
     }
@@ -132,6 +135,9 @@ class MatrixStorage<Scalar, RowsAtCompileTime, Dynamic>
     
     ~MatrixStorage()
     { delete[] m_data; }
+    
+  private:
+    MatrixStorage();
 };
 
 template<typename Scalar>
@@ -161,13 +167,17 @@ class MatrixStorage<Scalar, Dynamic, Dynamic>
     
   public:
     
-    MatrixStorage(int rows = 1, int cols = 1) : m_rows(rows), m_cols(cols)
+    MatrixStorage(int rows, int cols) : m_rows(rows), m_cols(cols)
     {
       m_data = new Scalar[m_rows * m_cols];
     }
     
     ~MatrixStorage()
     { delete[] m_data; }
+    
+  private:
+    MatrixStorage();
+    MatrixStorage(int dim);
 };
 
 #endif // EIGEN_MATRIXSTORAGE_H