eigen/Eigen/src/Core/Eval.h

// This file is part of Eigen, a lightweight C++ template library
// for linear algebra. Eigen itself is part of the KDE project.
//
// Copyright (C) 2006-2007 Benoit Jacob <jacob@math.jussieu.fr>
//
// Eigen is free software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the Free Software
// Foundation; either version 2 or (at your option) any later version.
//
// Eigen is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
// FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
// details.
//
// You should have received a copy of the GNU General Public License along
// with Eigen; if not, write to the Free Software Foundation, Inc., 51
// Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
//
// As a special exception, if other files instantiate templates or use macros
// or functions from this file, or you compile this file and link it
// with other works to produce a work based on this file, this file does not
// by itself cause the resulting work to be covered by the GNU General Public
// License. This exception does not invalidate any other reasons why a work
// based on this file might be covered by the GNU General Public License.

#ifndef EIGEN_EVAL_H
#define EIGEN_EVAL_H

/** \class Eval
  *
  * \brief Evaluation of an expression
  *
  * The template parameter Expression is the type of the expression that we are evaluating.
  *
  * This class is the return
  * type of MatrixBase::eval() and most of the time this is the only way it
  * is used.
  *
  * However, if you want to write a function returning an evaluation of an expression, you
  * will need to use this class.
  *
  * Here is an example illustrating this:
  * \include class_Eval.cpp
  * Output: \verbinclude class_Eval.out
  *
  * \sa MatrixBase::eval()
  */
template<typename Expression> class Eval : NoOperatorEquals,
  public Matrix< typename Expression::Scalar,
                 Expression::Traits::RowsAtCompileTime,
                 Expression::Traits::ColsAtCompileTime >
{
  public:
    typedef typename Expression::Scalar Scalar;
    typedef Matrix<Scalar, Expression::Traits::RowsAtCompileTime, Expression::Traits::ColsAtCompileTime> MatrixType;
    typedef Expression Base;
    friend class MatrixBase<Scalar, Expression>;
    
    Eval(const Expression& expression) : MatrixType(expression) {}
};

/** Evaluates *this, which can be any expression, and returns the obtained matrix.
  *
  * A common use case for this is the following. In an expression-templates library
  * like Eigen, the coefficients of an expression are only computed as they are
  * accessed, they are not computed when the expression itself is constructed. This is
  * usually a good thing, as this "lazy evaluation" improves performance, but can also
  * in certain cases lead to wrong results and/or to redundant computations. In such
  * cases, one can restore the classical immediate-evaluation behavior by calling eval().
  *
  * Example: \include MatrixBase_eval.cpp
  * Output: \verbinclude MatrixBase_eval.out
  *
  * \sa class Eval */
template<typename Scalar, typename Derived>
const Eval<Derived> MatrixBase<Scalar, Derived>::eval() const
{
  return Eval<Derived>(*static_cast<const Derived*>(this));
}

#endif // EIGEN_EVAL_H