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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 (at) inria.fr>
      5 // Copyright (C) 2009-2010 Benoit Jacob <jacob.benoit.1 (at) 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