ExpressionBase.h

Go to the documentation of this file.

// ========================================================================= //
// This file is part of MyraMath, copyright (c) 2014-2019 by Ryan A Chilton  //
// and distributed by MyraCore, LLC. See LICENSE.txt for license terms.      //
// ========================================================================= //

#ifndef MYRAMATH_EXPRESSION_EXPRESSIONBASE_H
#define MYRAMATH_EXPRESSION_EXPRESSIONBASE_H

#include <myramath/MYRAMATH_EXPORT.h>
#include <myramath/utility/Number.h>

#include <myramath/expression/Index.h>

namespace myra {

// Forward declarations.
template<int Arity, class Number> class Expression;

namespace detail {

// Implementation detail. Base class for all Expression's.
template<int Arity, class Number> class MYRAMATH_EXPORT ExpressionBase
  {
  protected:

    virtual Index<Arity> size() const = 0;
  
    virtual Number evaluate(Index<Arity> i) const = 0;

    // Virtual destructor, so subtypes can release resources.
    virtual ~ExpressionBase();

    // Virtual copy constructor.
    virtual ExpressionBase<Arity,Number>* clone() const = 0;

    // Friendship for encapsulating Expression, so it can clone()/copy.
    friend class ::myra::Expression<Arity,Number>;
  
  };

// Default constructed value of an Expression, does nothing.
template<int Arity, class Number> class NullExpression : public ExpressionBase<Arity,Number>
  {
  public:
  
    // Default constructor.
    NullExpression()
      { }

  protected:
  
    // Size inspector.
    virtual Index<Arity> size() const
      { return Index<Arity>(); }
  
    // Given an Index i, returns a Number.
    virtual Number evaluate(Index<Arity> i) const
      { return Number(0); }
 
    // Virtual copy constructor.
    virtual ExpressionBase<Arity,Number>* clone() const
      { return new NullExpression<Arity,Number>(); }
    
  };

} // namespace detail

} // namespace

#endif