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///////////////////////////////////////////////////////////////////////////////
// Name: wx/private/extfield.h
// Purpose: Declare wxExternalField helper
// Author: Vadim Zeitlin
// Created: 2017-11-21
// Copyright: (c) 2017 Vadim Zeitlin <vadim@wxwidgets.org>
// Licence: wxWindows licence
///////////////////////////////////////////////////////////////////////////////
#ifndef _WX_PRIVATE_EXTFIELD_H_
#define _WX_PRIVATE_EXTFIELD_H_
// ----------------------------------------------------------------------------
// wxExternalField: store object data outside of it
// ----------------------------------------------------------------------------
// This class allows to store some data without consuming space for the objects
// that don't need it and can be useful for avoiding to add rarely used fields
// to the classes that are used by many objects, e.g. wxWindow.
//
// Note that using this class costs in speed and convenience of access to the
// field, which requires a hash lookup instead of accessing it directly. It
// also only currently works for heap-allocated fields as it's probably never
// worth using it for fields of simple types.
//
// Template parameter Object is the class that "contains" the field, Field is
// the type of the field itself and FieldMap is the hash map, defined
// separately using WX_DECLARE_HASH_MAP(), with Object* as the key and Field*
// as the value type.
template <typename Object, typename Field, typename FieldMap>
class wxExternalField
{
public:
typedef Object ObjectType;
typedef Field FieldType;
typedef FieldMap MapType;
// Store the field object to be used for the given object, replacing the
// existing one, if any.
//
// This method takes ownership of the field pointer which will be destroyed
// by EraseForObject().
static void StoreForObject(ObjectType* obj, FieldType* field)
{
const typename MapType::iterator it = ms_map.find(obj);
if ( it != ms_map.end() )
{
delete it->second;
it->second = field;
}
else
{
ms_map.insert(typename MapType::value_type(obj, field));
}
}
// Find the object for the corresponding window.
static FieldType* FromObject(ObjectType* obj)
{
const typename MapType::const_iterator it = ms_map.find(obj);
return it == ms_map.end() ? NULL : it->second;
}
// Erase the object used for the corresponding window, return true if there
// was one or false otherwise.
static bool EraseForObject(ObjectType* obj)
{
const typename MapType::iterator it = ms_map.find(obj);
if ( it == ms_map.end() )
return false;
delete it->second;
ms_map.erase(it);
return true;
}
private:
static FieldMap ms_map;
};
template <typename O, typename F, typename M>
M wxExternalField<O, F, M>::ms_map;
#endif // _WX_PRIVATE_EXTFIELD_H_
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