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 namespace internal {
17 
18 template<typename Derived>
19 struct traits<ReturnByValue<Derived> >
20   : public traits<typename traits<Derived>::ReturnType>
21 {
22   enum {
23     // We're disabling the DirectAccess because e.g. the constructor of
24     // the Block-with-DirectAccess expression requires to have a coeffRef method.
25     // Also, we don't want to have to implement the stride stuff.
26     Flags = (traits<typename traits<Derived>::ReturnType>::Flags
27              | EvalBeforeNestingBit) & ~DirectAccessBit
28   };
29 };
30 
31 /* The ReturnByValue object doesn't even have a coeff() method.
32  * So the only way that nesting it in an expression can work, is by evaluating it into a plain matrix.
33  * So internal::nested always gives the plain return matrix type.
34  *
35  * FIXME: I don't understand why we need this specialization: isn't this taken care of by the EvalBeforeNestingBit ??
36  * Answer: EvalBeforeNestingBit should be deprecated since we have the evaluators
37  */
38 template<typename Derived,int n,typename PlainObject>
39 struct nested_eval<ReturnByValue<Derived>, n, PlainObject>
40 {
41   typedef typename traits<Derived>::ReturnType type;
42 };
43 
44 } // end namespace internal
45 
46 /** \class ReturnByValue
47   * \ingroup Core_Module
48   *
49   */
50 template<typename Derived> class ReturnByValue
51   : public internal::dense_xpr_base< ReturnByValue<Derived> >::type, internal::no_assignment_operator
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     EIGEN_DEVICE_FUNC
61     inline void evalTo(Dest& dst) const
62     { static_cast<const Derived*>(this)->evalTo(dst); }
63     EIGEN_DEVICE_FUNC inline Index rows() const { return static_cast<const Derived*>(this)->rows(); }
64     EIGEN_DEVICE_FUNC inline Index cols() const { return static_cast<const Derived*>(this)->cols(); }
65 
66 #ifndef EIGEN_PARSED_BY_DOXYGEN
67 #define Unusable YOU_ARE_TRYING_TO_ACCESS_A_SINGLE_COEFFICIENT_IN_A_SPECIAL_EXPRESSION_WHERE_THAT_IS_NOT_ALLOWED_BECAUSE_THAT_WOULD_BE_INEFFICIENT
68     class Unusable{
69       Unusable(const Unusable&) {}
70       Unusable& operator=(const Unusable&) {return *this;}
71     };
72     const Unusable& coeff(Index) const { return *reinterpret_cast<const Unusable*>(this); }
73     const Unusable& coeff(Index,Index) const { return *reinterpret_cast<const Unusable*>(this); }
74     Unusable& coeffRef(Index) { return *reinterpret_cast<Unusable*>(this); }
75     Unusable& coeffRef(Index,Index) { return *reinterpret_cast<Unusable*>(this); }
76 #undef Unusable
77 #endif
78 };
79 
80 template<typename Derived>
81 template<typename OtherDerived>
82 Derived& DenseBase<Derived>::operator=(const ReturnByValue<OtherDerived>& other)
83 {
84   other.evalTo(derived());
85   return derived();
86 }
87 
88 namespace internal {
89 
90 // Expression is evaluated in a temporary; default implementation of Assignment is bypassed so that
91 // when a ReturnByValue expression is assigned, the evaluator is not constructed.
92 // TODO: Finalize port to new regime; ReturnByValue should not exist in the expression world
93 
94 template<typename Derived>
95 struct evaluator<ReturnByValue<Derived> >
96   : public evaluator<typename internal::traits<Derived>::ReturnType>
97 {
98   typedef ReturnByValue<Derived> XprType;
99   typedef typename internal::traits<Derived>::ReturnType PlainObject;
100   typedef evaluator<PlainObject> Base;
101 
102   EIGEN_DEVICE_FUNC explicit evaluator(const XprType& xpr)
103     : m_result(xpr.rows(), xpr.cols())
104   {
105     ::new (static_cast<Base*>(this)) Base(m_result);
106     xpr.evalTo(m_result);
107   }
108 
109 protected:
110   PlainObject m_result;
111 };
112 
113 } // end namespace internal
114 
115 } // end namespace Eigen
116 
117 #endif // EIGEN_RETURNBYVALUE_H
118