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/////////////////////////////////////////////////////////////////////////////
// Name: wx/meta/if.h
// Purpose: declares wxIf<> metaprogramming construct
// Author: Vaclav Slavik
// Created: 2008-01-22
// Copyright: (c) 2008 Vaclav Slavik
// Licence: wxWindows licence
/////////////////////////////////////////////////////////////////////////////
#ifndef _WX_META_IF_H_
#define _WX_META_IF_H_
#include "wx/defs.h"
// NB: This code is intentionally written without partial templates
// specialization, because some older compilers (notably VC6) don't
// support it.
namespace wxPrivate
{
template <bool Cond>
struct wxIfImpl
// broken VC6 needs not just an incomplete template class declaration but a
// "skeleton" declaration of the specialized versions below as it apparently
// tries to look up the types in the generic template definition at some moment
// even though it ends up by using the correct specialization in the end -- but
// without this skeleton it doesn't recognize Result as a class at all below
#if defined(__VISUALC__) && !wxCHECK_VISUALC_VERSION(7)
{
template<typename TTrue, typename TFalse> struct Result {};
}
#endif // VC++ <= 6
;
// specialization for true:
template <>
struct wxIfImpl<true>
{
template<typename TTrue, typename TFalse> struct Result
{
typedef TTrue value;
};
};
// specialization for false:
template<>
struct wxIfImpl<false>
{
template<typename TTrue, typename TFalse> struct Result
{
typedef TFalse value;
};
};
} // namespace wxPrivate
// wxIf<> template defines nested type "value" which is the same as
// TTrue if the condition Cond (boolean compile-time constant) was met and
// TFalse if it wasn't.
//
// See wxVector<T> in vector.h for usage example
template<bool Cond, typename TTrue, typename TFalse>
struct wxIf
{
typedef typename wxPrivate::wxIfImpl<Cond>
::template Result<TTrue, TFalse>::value
value;
};
#endif // _WX_META_IF_H_
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