From 113fc3a2606997533287921ccec49e320bf9f79b Mon Sep 17 00:00:00 2001
From: Benoit Jacob <jacob.benoit.1@gmail.com>
Date: Wed, 1 Apr 2009 00:39:56 +0000
Subject: [PATCH] now if Derived has the DirectAccess flag, then
 MatrixBase<Derived>::coeff() const returns a const Scalar& and not a Scalar
 as before. useful for people doing direct access. + 1 bugfix thanks to
 Patrick Mihelich, forgot a & in MapBase::coeff(int).

---
 Eigen/src/Core/Coeffs.h     | 18 +++++++++---------
 Eigen/src/Core/MapBase.h    |  2 +-
 Eigen/src/Core/MatrixBase.h | 22 +++++++++++++---------
 3 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/Eigen/src/Core/Coeffs.h b/Eigen/src/Core/Coeffs.h
index 23a84228b..b514dcd17 100644
--- a/Eigen/src/Core/Coeffs.h
+++ b/Eigen/src/Core/Coeffs.h
@@ -40,7 +40,7 @@
   * \sa operator()(int,int) const, coeffRef(int,int), coeff(int) const
   */
 template<typename Derived>
-EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
+EIGEN_STRONG_INLINE const typename MatrixBase<Derived>::CoeffReturnType MatrixBase<Derived>
   ::coeff(int row, int col) const
 {
   ei_internal_assert(row >= 0 && row < rows()
@@ -53,7 +53,7 @@ EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived
   * \sa operator()(int,int), operator[](int) const
   */
 template<typename Derived>
-EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
+EIGEN_STRONG_INLINE const typename MatrixBase<Derived>::CoeffReturnType MatrixBase<Derived>
   ::operator()(int row, int col) const
 {
   ei_assert(row >= 0 && row < rows()
@@ -112,7 +112,7 @@ EIGEN_STRONG_INLINE typename ei_traits<Derived>::Scalar& MatrixBase<Derived>
   * \sa operator[](int) const, coeffRef(int), coeff(int,int) const
   */
 template<typename Derived>
-EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
+EIGEN_STRONG_INLINE const typename MatrixBase<Derived>::CoeffReturnType MatrixBase<Derived>
   ::coeff(int index) const
 {
   ei_internal_assert(index >= 0 && index < size());
@@ -127,7 +127,7 @@ EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived
   * z() const, w() const
   */
 template<typename Derived>
-EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
+EIGEN_STRONG_INLINE const typename MatrixBase<Derived>::CoeffReturnType MatrixBase<Derived>
   ::operator[](int index) const
 {
   ei_assert(index >= 0 && index < size());
@@ -144,7 +144,7 @@ EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived
   * z() const, w() const
   */
 template<typename Derived>
-EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
+EIGEN_STRONG_INLINE const typename MatrixBase<Derived>::CoeffReturnType MatrixBase<Derived>
   ::operator()(int index) const
 {
   ei_assert(index >= 0 && index < size());
@@ -205,22 +205,22 @@ EIGEN_STRONG_INLINE typename ei_traits<Derived>::Scalar& MatrixBase<Derived>
 
 /** equivalent to operator[](0).  */
 template<typename Derived>
-EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
+EIGEN_STRONG_INLINE const typename MatrixBase<Derived>::CoeffReturnType MatrixBase<Derived>
   ::x() const { return (*this)[0]; }
 
 /** equivalent to operator[](1).  */
 template<typename Derived>
-EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
+EIGEN_STRONG_INLINE const typename MatrixBase<Derived>::CoeffReturnType MatrixBase<Derived>
   ::y() const { return (*this)[1]; }
 
 /** equivalent to operator[](2).  */
 template<typename Derived>
-EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
+EIGEN_STRONG_INLINE const typename MatrixBase<Derived>::CoeffReturnType MatrixBase<Derived>
   ::z() const { return (*this)[2]; }
 
 /** equivalent to operator[](3).  */
 template<typename Derived>
-EIGEN_STRONG_INLINE const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
+EIGEN_STRONG_INLINE const typename MatrixBase<Derived>::CoeffReturnType MatrixBase<Derived>
   ::w() const { return (*this)[3]; }
 
 /** equivalent to operator[](0).  */
diff --git a/Eigen/src/Core/MapBase.h b/Eigen/src/Core/MapBase.h
index ed3d2cbf8..bc666878a 100644
--- a/Eigen/src/Core/MapBase.h
+++ b/Eigen/src/Core/MapBase.h
@@ -96,7 +96,7 @@ template<typename Derived> class MapBase
         return const_cast<Scalar*>(m_data)[row + col * stride()];
     }
 
-    inline const Scalar coeff(int index) const
+    inline const Scalar& coeff(int index) const
     {
       ei_assert(Derived::IsVectorAtCompileTime || (ei_traits<Derived>::Flags & LinearAccessBit));
       if ( ((RowsAtCompileTime == 1) == IsRowMajor) )
diff --git a/Eigen/src/Core/MatrixBase.h b/Eigen/src/Core/MatrixBase.h
index dfe17c526..2d6b3d85b 100644
--- a/Eigen/src/Core/MatrixBase.h
+++ b/Eigen/src/Core/MatrixBase.h
@@ -199,6 +199,10 @@ template<typename Derived> class MatrixBase
       */
     typedef typename ei_plain_matrix_type<Derived>::type PlainMatrixType_ColMajor;
 
+    /** \internal the return type of coeff()
+      */
+    typedef typename ei_meta_if<int(Flags)&DirectAccessBit, const Scalar&, Scalar>::ret CoeffReturnType;
+
     /** \internal Represents a matrix with all coefficients equal to one another*/
     typedef CwiseNullaryOp<ei_scalar_constant_op<Scalar>,Derived> ConstantReturnType;
     /** \internal Represents a scalar multiple of a matrix */
@@ -264,15 +268,15 @@ template<typename Derived> class MatrixBase
     template<typename OtherDerived>
     CommaInitializer<Derived> operator<< (const MatrixBase<OtherDerived>& other);
 
-    const Scalar coeff(int row, int col) const;
-    const Scalar operator()(int row, int col) const;
+    const CoeffReturnType coeff(int row, int col) const;
+    const CoeffReturnType operator()(int row, int col) const;
 
     Scalar& coeffRef(int row, int col);
     Scalar& operator()(int row, int col);
 
-    const Scalar coeff(int index) const;
-    const Scalar operator[](int index) const;
-    const Scalar operator()(int index) const;
+    const CoeffReturnType coeff(int index) const;
+    const CoeffReturnType operator[](int index) const;
+    const CoeffReturnType operator()(int index) const;
 
     Scalar& coeffRef(int index);
     Scalar& operator[](int index);
@@ -299,10 +303,10 @@ template<typename Derived> class MatrixBase
     template<int StoreMode>
     void writePacket(int index, const PacketScalar& x);
 
-    const Scalar x() const;
-    const Scalar y() const;
-    const Scalar z() const;
-    const Scalar w() const;
+    const CoeffReturnType x() const;
+    const CoeffReturnType y() const;
+    const CoeffReturnType z() const;
+    const CoeffReturnType w() const;
     Scalar& x();
     Scalar& y();
     Scalar& z();