--- /dev/null
+/* ========================================================================
+** Extended Template and Library
+** Abstraction for a Generic Value Type
+** $Id$
+**
+** Copyright (c) 2002 Adrian Bentley
+**
+** This package 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 of
+** the License, or (at your option) any later version.
+**
+** This package 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.
+**
+** === N O T E S ===========================================================
+**
+** This is an internal header file, included by other ETL headers.
+** You should not attempt to use it directly.
+**
+** ========================================================================= */
+
+/* === S T A R T =========================================================== */
+
+#ifndef __ETL__VALUE_H
+#define __ETL__VALUE_H
+
+/* === H E A D E R S ======================================================= */
+#include <algorithm>
+#include <typeinfo>
+#include <cassert>
+
+/* === M A C R O S ========================================================= */
+
+/* === T Y P E D E F S ===================================================== */
+
+/* === C L A S S E S & S T R U C T S ======================================= */
+
+/*! \note This class may be specialized to support binary compatibility
+ for desired objects (e.g. point3,vector3,float[3]).
+ However it MUST be declared within scope that you are using the
+ values....
+
+ \warning If you specialize this class for something that isn't binary
+ compatible, then your values could easily report belonging to
+ the wrong types.
+*/
+template < typename T >
+class value_store_type
+{
+public:
+ typedef T value_type;
+};
+
+_ETL_BEGIN_NAMESPACE
+
+/*! \class value _value.h ETL/value
+ \brief Abstraction of the concept of a generic value
+
+ Modified from ideas for the boost::any type. Added binary compatibility
+ structure
+*/
+class value
+{
+ struct contentholder
+ {
+ virtual ~contentholder() {}
+ virtual contentholder *clone() const = 0;
+ virtual const std::type_info &type() const = 0;
+ };
+
+ contentholder *content;
+
+public: //constructor interface
+ value()
+ :content(0)
+ {
+ }
+
+ value(const value &v)
+ :content( v.content ? v.content->clone() : 0 )
+ {
+ }
+
+ /* Copies the object passed to it
+ */
+ template < typename T >
+ value(const T &v)
+ :content( new holder< typename value_store_type<T>::value_type >
+ (reinterpret_cast<const typename value_store_type<T>::value_type &>(v)) )
+ {
+ }
+
+public: //modifier interface
+
+ value & swap(value & rhs)
+ {
+ std::swap(content, rhs.content);
+ return *this;
+ }
+
+ template<typename ValueType>
+ value & operator=(const ValueType & rhs)
+ {
+ value(rhs).swap(*this);
+ return *this;
+ }
+
+ value & operator=(const value & rhs)
+ {
+ value(rhs).swap(*this);
+ return *this;
+ }
+
+public: //query interface
+
+ bool empty() const
+ {
+ return content == 0;
+ }
+
+ const std::type_info & type() const
+ {
+ return content ? content->type() : typeid(void);
+ }
+
+private: //implementation interface
+
+ template < typename T >
+ class holder : public contentholder
+ {
+ public: //representation
+ T obj;
+
+ public: //constructor interface
+
+ holder(const T &o)
+ :obj(o)
+ {
+ }
+
+ holder(const holder<T> &h)
+ :obj(h.obj)
+ {
+ }
+
+ public: //accessor interface
+ virtual contentholder *clone() const
+ {
+ return new holder(*this);
+ }
+
+ virtual const std::type_info &type() const
+ {
+ return typeid(T);
+ }
+
+ public: //allocation interface
+ void *operator new(unsigned int size)
+ {
+ assert(size == sizeof(holder<T>));
+
+ //use pool allocation at some point
+ return malloc(size);
+ }
+
+ void operator delete(void *p)
+ {
+ assert(p);
+ //use pool allocation at some point
+ return free(p);
+ }
+ };
+
+ template < typename ValueType >
+ friend ValueType *value_cast(value *v);
+};
+
+/*! Is thrown for bad value_casts (when using a reference...)
+*/
+class bad_value_cast : public std::bad_cast
+{
+public:
+ virtual const char * what() const throw()
+ {
+ return "etl::bad_value_cast: " "failed conversion using boost::value_cast";
+ }
+};
+
+/*! Returns a pointer to the desired value type if the value_type and the internal
+ binary format agree (mediated by using the value_store_type class), otherwise
+ it returns 0.
+
+ \see value_store_type
+*/
+template < typename ValueType >
+ValueType *value_cast(value *v)
+{
+ assert(v);
+
+ return ( typeid(typename value_store_type<ValueType>::value_type) == v->type() )
+ ? &static_cast<value::holder<ValueType> *>(v->content)->obj
+ : 0;
+}
+
+/*! Same as above except tweaked to allow const cast (possibly for purposes involving
+ type agreement... if const impacts a typeid call I do not know...)
+*/
+template < typename ValueType >
+const ValueType * value_cast(const value *v)
+{
+ return value_cast<ValueType>(const_cast<value *>(v));
+}
+
+/*! Extract a copy of the internal object and will throw a bad_value_cast exception
+ if the types do not agree.
+
+ \note I'm not sure why boost::any didn't use a reference here... there must be a reason...
+
+ \see bad_value_cast
+*/
+template < typename ValueType >
+ValueType value_cast(const value &v)
+{
+ const ValueType * result = value_cast<ValueType>(&v);
+ if(!result)
+ throw bad_value_cast();
+ return *result;
+}
+
+_ETL_END_NAMESPACE
+
+/* === E N D =============================================================== */
+
+#endif
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