From 7029ed6b8830937d3674064a3945642c99cb658f Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Wed, 29 Apr 2009 17:39:39 +0000
Subject: [PATCH] ok, this time cast should really work ; sorry for the noise

---
 Eigen/src/Core/DiagonalMatrix.h | 21 +++++++++++++++++++--
 Eigen/src/Core/util/XprHelper.h |  8 ++++++--
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/Eigen/src/Core/DiagonalMatrix.h b/Eigen/src/Core/DiagonalMatrix.h
index a95a45eb3..57f92a968 100644
--- a/Eigen/src/Core/DiagonalMatrix.h
+++ b/Eigen/src/Core/DiagonalMatrix.h
@@ -70,6 +70,22 @@ class DiagonalMatrixBase : ei_no_assignment_operator,
       construct_from_expression<OtherDerived,OtherDerived::IsVectorAtCompileTime,(OtherDerived::Flags&Diagonal)==Diagonal>
         ::run(derived(),other.derived());
     }
+    
+    template<typename NewType,int dummy=0>
+    struct cast_selector {
+      typedef const DiagonalMatrixWrapper<NestByValue<CwiseUnaryOp<ei_scalar_cast_op<Scalar, NewType>, _CoeffsVectorType> > > return_type;
+      inline static return_type run(const DiagonalMatrixBase& d) {
+        return d.m_coeffs.template cast<NewType>().nestByValue().asDiagonal();
+      }
+    };
+    
+    template<int dummy>
+    struct cast_selector<Scalar,dummy> {
+      typedef const Derived& return_type;
+      inline static return_type run(const DiagonalMatrixBase& d) {
+        return d.derived();
+      }
+    };
 
   public:
 
@@ -80,9 +96,10 @@ class DiagonalMatrixBase : ei_no_assignment_operator,
     }
 
     template<typename NewType>
-    inline DiagonalMatrixWrapper<NestByValue<CwiseUnaryOp<ei_scalar_cast_op<Scalar, NewType>, _CoeffsVectorType> > > cast() const
+    inline typename cast_selector<NewType,0>::return_type
+    cast() const
     {
-      return m_coeffs.template cast<NewType>().nestByValue().asDiagonal();
+      return cast_selector<NewType,0>::run(*this);
     }
 
     /** Assignment operator.
diff --git a/Eigen/src/Core/util/XprHelper.h b/Eigen/src/Core/util/XprHelper.h
index 857722b79..6ffe14762 100644
--- a/Eigen/src/Core/util/XprHelper.h
+++ b/Eigen/src/Core/util/XprHelper.h
@@ -242,9 +242,13 @@ template<typename ExpressionType> struct HNormalizedReturnType {
               NestByValue<StartMinusOne> > Type;
 };
 
-template<typename CurrentType, typename NewType> struct ei_cast_return_type
+template<typename XprType, typename CastType> struct ei_cast_return_type
 {
-  typedef typename ei_meta_if<ei_is_same_type<CurrentType,NewType>::ret,const CurrentType&,NewType>::ret type;
+  typedef typename XprType::Scalar CurrentScalarType;
+  typedef typename ei_cleantype<CastType>::type _CastType;
+  typedef typename _CastType::Scalar NewScalarType;
+  typedef typename ei_meta_if<ei_is_same_type<CurrentScalarType,NewScalarType>::ret,
+                              const XprType&,CastType>::ret type;
 };
 
 #endif // EIGEN_XPRHELPER_H