pany.h

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/*
 *   P::Classes - Portable C++ Application Framework
 *   Copyright (C) 2000-2003  Christian Prochnow <cproch@seculogix.de>
 *
 *   This library is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU Lesser General Public
 *   License as published by the Free Software Foundation; either
 *   version 2 of the License, or (at your option) any later version.
 *
 *   This library 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
 *   Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 *   Based on boost::any Copyright Kevlin Henney, 2000, 2001, 2002. All rights reserved.
 */

#ifndef _pany_h_
#define _pany_h_

#include <algorithm>
#include <typeinfo>
#include <iostream>

namespace P {


class Any {
  public:
    Any()
    : m_data(0)
    { }

    Any(const Any& val)
    : m_data(val.m_data ? val.m_data->clone() : 0)
    { }

    template <typename ValueType>
    Any(const ValueType& val)
    : m_data(new holder<ValueType>(val))
    { }

    ~Any()
    {
      if(m_data)
        delete m_data;
    }

    Any& swap(Any& rhs)
    {
      std::swap(m_data, rhs.m_data);
      return *this;
    }

    template <typename ValueType>
    Any& operator=(const ValueType& rhs)
    {
      Any(rhs).swap(*this);
      return *this;
    }

    Any& operator=(const Any& rhs)
    {
      Any(rhs).swap(*this);
      return *this;
    }

    inline bool empty() const
    { return !m_data; }

    const std::type_info& type() const
    { return m_data ? m_data->type() : typeid(void); }

    template <typename ValueType>
    friend ValueType* any_cast(Any* val);

    friend std::ostream& operator<<(std::ostream& os, const Any& val);

  private:

    class holder_iface {
      public:
        virtual ~holder_iface()
        { }

        virtual const std::type_info& type() const = 0;
        virtual holder_iface* clone() const = 0;
        virtual void output(std::ostream& os) const = 0;
    };

    template <typename ValueType>
    class holder: public holder_iface {
      public:
        holder(const ValueType& val)
        : m_value(val)
        { }

        virtual const std::type_info& type() const
        { return typeid(ValueType); }

        virtual holder_iface* clone() const
        { return new holder(m_value); }

        virtual void output(std::ostream& os) const
        { os << m_value; }

      private:
        ValueType m_value;
    };

  private:
    holder_iface* m_data;

};


class BadAnyCast: public std::bad_cast {
  public:
    virtual const char* what() const throw()
    { return "BadAnyCast: failed conversion using P::any_cast"; }
};


template <typename ValueType>
ValueType* any_cast(Any* operand)
{
  return operand && operand->type() == typeid(ValueType) ?
    &static_cast<Any::holder<ValueType>*>(operand->m_data)->m_value : 0;
}


template <typename ValueType>
const ValueType* any_cast(const Any* operand)
{
  return any_cast<ValueType>(const_cast<Any*>(operand));
}


template <typename ValueType>
ValueType any_cast(const Any& operand) throw(BadAnyCast)
{
  const ValueType* result = any_cast<ValueType>(&operand);
  if(!result)
    throw BadAnyCast();

  return *result;
}


std::ostream& operator<<(std::ostream& os, const Any& val)
{
  val.m_data->output(os);
  return os;
}

}

#endif

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