add cast<newtype>() function to casts the scalars to another type.

src/Core.h

@@ -11,6 +11,7 @@ namespace Eigen {
 #include "Core/MatrixRef.h"
 #include "Core/MatrixStorage.h"
 #include "Core/Matrix.h"
+#include "Core/Cast.h"
 #include "Core/Eval.h"
 #include "Core/ScalarMultiple.h"
 #include "Core/Sum.h"

src/Core/Cast.h

@@ -0,0 +1,70 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra. Eigen itself is part of the KDE project.
+//
+// Copyright (C) 2006-2007 Benoit Jacob <jacob@math.jussieu.fr>
+//
+// Eigen is free software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the Free Software
+// Foundation; either version 2 or (at your option) any later version.
+//
+// Eigen is distributed in the hope that it will be useful, but WITHOUT ANY
+// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+// details.
+//
+// You should have received a copy of the GNU General Public License along
+// with Eigen; if not, write to the Free Software Foundation, Inc., 51
+// Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+//
+// As a special exception, if other files instantiate templates or use macros
+// or functions from this file, or you compile this file and link it
+// with other works to produce a work based on this file, this file does not
+// by itself cause the resulting work to be covered by the GNU General Public
+// License. This exception does not invalidate any other reasons why a work
+// based on this file might be covered by the GNU General Public License.
+
+#ifndef EI_CAST_H
+#define EI_CAST_H
+
+template<typename NewScalar, typename MatrixType> class Cast
+  : public Object<NewScalar, Cast<NewScalar, MatrixType> >
+{
+  public:
+    typedef NewScalar Scalar;
+    typedef typename MatrixType::Ref MatRef;
+    friend class Object<Scalar, Cast<Scalar, MatrixType> >;
+    
+    static const int RowsAtCompileTime = MatrixType::RowsAtCompileTime,
+                     ColsAtCompileTime = MatrixType::ColsAtCompileTime;
+
+    Cast(const MatRef& matrix) : m_matrix(matrix) {}
+    
+    Cast(const Cast& other)
+      : m_matrix(other.m_matrix) {}
+    
+    // assignments are illegal but we still want to intercept them and get clean compile errors
+    EI_INHERIT_ASSIGNMENT_OPERATORS(Cast)
+    
+  private:
+    const Cast& _ref() const { return *this; }
+    int _rows() const { return m_matrix.rows(); }
+    int _cols() const { return m_matrix.cols(); }
+    
+    Scalar _read(int row, int col) const
+    {
+      return static_cast<Scalar>(m_matrix.read(row, col));
+    }
+    
+  protected:
+    MatRef m_matrix;
+};
+
+template<typename Scalar, typename Derived>
+template<typename NewScalar>
+Cast<NewScalar, Derived>
+Object<Scalar, Derived>::cast() const
+{
+  return Cast<NewScalar, Derived>(static_cast<const Derived*>(this)->ref());
+}
+
+#endif // EI_CAST_H

src/Core/Conjugate.h

@@ -42,6 +42,7 @@ template<typename MatrixType> class Conjugate
     Conjugate(const Conjugate& other)
       : m_matrix(other.m_matrix) {}
     
+   // assignments are illegal but we still want to intercept them and get clean compile errors
    EI_INHERIT_ASSIGNMENT_OPERATORS(Conjugate)
     
   private:

src/Core/Object.h

@@ -91,6 +91,8 @@ template<typename Scalar, typename Derived> class Object
       return *static_cast<Derived*>(this);
     }
     
+    template<typename NewScalar> Cast<NewScalar, Derived> cast() const;
+    
     Row<Derived> row(int i) const;
     Column<Derived> col(int i) const;
     Minor<Derived> minor(int row, int col) const;
@@ -102,7 +104,6 @@ template<typename Scalar, typename Derived> class Object
     
     template<typename OtherDerived>
     Scalar dot(const OtherDerived& other) const;
-    
     RealScalar norm2() const;
     RealScalar norm()  const;
     ScalarMultiple<Derived> normalized() const;

src/Core/Util.h

@@ -43,6 +43,7 @@ using Eigen::Matrix;
 //forward declarations
 template<typename _Scalar, int _Rows, int _Cols> class Matrix;
 template<typename MatrixType> class MatrixRef;
+template<typename NewScalar, typename MatrixType> class Cast;
 template<typename MatrixType> class Row;
 template<typename MatrixType> class Column;
 template<typename MatrixType> class Minor;