wxWidgets/include/wx/meta/movable.h

/////////////////////////////////////////////////////////////////////////////
// Name:        wx/meta/movable.h
// Purpose:     Test if a type is movable using memmove() etc.
// Author:      Vaclav Slavik
// Created:     2008-01-21
// RCS-ID:      $Id$
// Copyright:   (c) 2008 Vaclav Slavik
// Licence:     wxWindows licence
/////////////////////////////////////////////////////////////////////////////

#ifndef _WX_META_MOVABLE_H_
#define _WX_META_MOVABLE_H_

#include "wx/defs.h"
#include "wx/string.h" // for wxIsMovable<wxString> specialization

// This macro declares something called "value" inside a class declaration.
//
// It has to be used because VC6 doesn't handle initialization of the static
// variables in the class declaration itself while BCC5.82 doesn't understand
// enums (it compiles the template fine but can't use it later)
#if defined(__VISUALC__) && !wxCHECK_VISUALC_VERSION(7)
    #define wxDEFINE_TEMPLATE_BOOL_VALUE(val) enum { value = val }
#else
    #define wxDEFINE_TEMPLATE_BOOL_VALUE(val) static const bool value = val
#endif

// Helper to decide if an object of type T is "movable", i.e. if it can be
// copied to another memory location using memmove() or realloc() C functions.
// C++ only gurantees that POD types (including primitive types) are
// movable.
template<typename T>
struct wxIsMovable
{
    wxDEFINE_TEMPLATE_BOOL_VALUE(false);
};

// Macro to add wxIsMovable<T> specialization for given type that marks it
// as movable:
#define WX_DECLARE_TYPE_MOVABLE(type)                       \
    template<> struct wxIsMovable<type>                     \
    {                                                       \
        wxDEFINE_TEMPLATE_BOOL_VALUE(true);                 \
    };

WX_DECLARE_TYPE_MOVABLE(bool)
WX_DECLARE_TYPE_MOVABLE(unsigned char)
WX_DECLARE_TYPE_MOVABLE(signed char)
WX_DECLARE_TYPE_MOVABLE(unsigned int)
WX_DECLARE_TYPE_MOVABLE(signed int)
WX_DECLARE_TYPE_MOVABLE(unsigned short int)
WX_DECLARE_TYPE_MOVABLE(signed short int)
WX_DECLARE_TYPE_MOVABLE(signed long int)
WX_DECLARE_TYPE_MOVABLE(unsigned long int)
WX_DECLARE_TYPE_MOVABLE(float)
WX_DECLARE_TYPE_MOVABLE(double)
WX_DECLARE_TYPE_MOVABLE(long double)
#if wxWCHAR_T_IS_REAL_TYPE
WX_DECLARE_TYPE_MOVABLE(wchar_t)
#endif
#ifdef wxLongLong_t
WX_DECLARE_TYPE_MOVABLE(wxLongLong_t)
WX_DECLARE_TYPE_MOVABLE(wxULongLong_t)
#endif

// Visual C++ 6.0 can't compile partial template specializations and as this is
// only an optimization, we can live with pointers not being recognized as
// movable types under VC6
#if !defined(__VISUALC__) || wxCHECK_VISUALC_VERSION(7)

// pointers are movable:
template<typename T>
struct wxIsMovable<T*>
{
    static const bool value = true;
};

template<typename T>
struct wxIsMovable<const T*>
{
    static const bool value = true;
};

#endif // !VC++ < 7

// Our implementation of wxString is written in such way that it's safe to move
// it around (unless position cache is used which unfortunately breaks this).
// OTOH, we don't know anything about std::string.
// (NB: we don't put this into string.h and choose to include wx/string.h from
// here instead so that rarely-used wxIsMovable<T> code isn't included by
// everything)
#if !wxUSE_STL && !wxUSE_STRING_POS_CACHE
WX_DECLARE_TYPE_MOVABLE(wxString)
#endif

#endif // _WX_META_MOVABLE_H_