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1 // This file is part of Eigen, a lightweight C++ template library
2 // for linear algebra.
3 //
4 // Copyright (C) 2009-2010 Gael Guennebaud <gael.guennebaud@inria.fr>
5 // Copyright (C) 2009-2010 Benoit Jacob <jacob.benoit.1@gmail.com>
6 //
7 // This Source Code Form is subject to the terms of the Mozilla
8 // Public License v. 2.0. If a copy of the MPL was not distributed
9 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
10 
11 #ifndef EIGEN_RETURNBYVALUE_H
12 #define EIGEN_RETURNBYVALUE_H
13 
14 namespace Eigen {
15 
16 /** \class ReturnByValue
17   * \ingroup Core_Module
18   *
19   */
20 
21 namespace internal {
22 
23 template<typename Derived>
24 struct traits<ReturnByValue<Derived> >
25   : public traits<typename traits<Derived>::ReturnType>
26 {
27   enum {
28     // We're disabling the DirectAccess because e.g. the constructor of
29     // the Block-with-DirectAccess expression requires to have a coeffRef method.
30     // Also, we don't want to have to implement the stride stuff.
31     Flags = (traits<typename traits<Derived>::ReturnType>::Flags
32              | EvalBeforeNestingBit) & ~DirectAccessBit
33   };
34 };
35 
36 /* The ReturnByValue object doesn't even have a coeff() method.
37  * So the only way that nesting it in an expression can work, is by evaluating it into a plain matrix.
38  * So internal::nested always gives the plain return matrix type.
39  *
40  * FIXME: I don't understand why we need this specialization: isn't this taken care of by the EvalBeforeNestingBit ??
41  */
42 template<typename Derived,int n,typename PlainObject>
43 struct nested<ReturnByValue<Derived>, n, PlainObject>
44 {
45   typedef typename traits<Derived>::ReturnType type;
46 };
47 
48 } // end namespace internal
49 
50 template<typename Derived> class ReturnByValue
51   : internal::no_assignment_operator, public internal::dense_xpr_base< ReturnByValue<Derived> >::type
52 {
53   public:
54     typedef typename internal::traits<Derived>::ReturnType ReturnType;
55 
56     typedef typename internal::dense_xpr_base<ReturnByValue>::type Base;
57     EIGEN_DENSE_PUBLIC_INTERFACE(ReturnByValue)
58 
59     template<typename Dest>
60     inline void evalTo(Dest& dst) const
61     { static_cast<const Derived*>(this)->evalTo(dst); }
62     inline Index rows() const { return static_cast<const Derived*>(this)->rows(); }
63     inline Index cols() const { return static_cast<const Derived*>(this)->cols(); }
64 
65 #ifndef EIGEN_PARSED_BY_DOXYGEN
66 #define Unusable YOU_ARE_TRYING_TO_ACCESS_A_SINGLE_COEFFICIENT_IN_A_SPECIAL_EXPRESSION_WHERE_THAT_IS_NOT_ALLOWED_BECAUSE_THAT_WOULD_BE_INEFFICIENT
67     class Unusable{
68       Unusable(const Unusable&) {}
69       Unusable& operator=(const Unusable&) {return *this;}
70     };
71     const Unusable& coeff(Index) const { return *reinterpret_cast<const Unusable*>(this); }
72     const Unusable& coeff(Index,Index) const { return *reinterpret_cast<const Unusable*>(this); }
73     Unusable& coeffRef(Index) { return *reinterpret_cast<Unusable*>(this); }
74     Unusable& coeffRef(Index,Index) { return *reinterpret_cast<Unusable*>(this); }
75 #endif
76 };
77 
78 template<typename Derived>
79 template<typename OtherDerived>
80 Derived& DenseBase<Derived>::operator=(const ReturnByValue<OtherDerived>& other)
81 {
82   other.evalTo(derived());
83   return derived();
84 }
85 
86 } // end namespace Eigen
87 
88 #endif // EIGEN_RETURNBYVALUE_H
89