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