ReturnByValue.h revision 7faaa9f3f0df9d23790277834d426c3d992ac3ba 
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
14namespace Eigen {
15
16/** \class ReturnByValue
17  * \ingroup Core_Module
18  *
19  */
20
21namespace internal {
22
23template<typename Derived>
24struct 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 */
42template<typename Derived,int n,typename PlainObject>
43struct nested<ReturnByValue<Derived>, n, PlainObject>
44{
45  typedef typename traits<Derived>::ReturnType type;
46};
47
48} // end namespace internal
49
50template<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
78template<typename Derived>
79template<typename OtherDerived>
80Derived& 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