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1 | ///////////////////////////////////////////////////////////////////////////// | |
2 | // Name: wx/meta/if.h | |
3 | // Purpose: declares wxIf<> metaprogramming construct | |
4 | // Author: Vaclav Slavik | |
5 | // Created: 2008-01-22 | |
6 | // RCS-ID: $Id$ | |
7 | // Copyright: (c) 2008 Vaclav Slavik | |
8 | // Licence: wxWindows licence | |
9 | ///////////////////////////////////////////////////////////////////////////// | |
10 | ||
11 | #ifndef _WX_META_IF_H_ | |
12 | #define _WX_META_IF_H_ | |
13 | ||
14 | #include "wx/defs.h" | |
15 | ||
16 | // NB: This code is intentionally written without partial templates | |
17 | // specialization, because some older compilers (notably VC6) don't | |
18 | // support it. | |
19 | ||
20 | namespace wxPrivate | |
21 | { | |
22 | ||
23 | template <bool Cond> | |
24 | struct wxIfImpl | |
25 | ||
26 | // broken VC6 needs not just an incomplete template class declaration but a | |
27 | // "skeleton" declaration of the specialized versions below as it apparently | |
28 | // tries to look up the types in the generic template definition at some moment | |
29 | // even though it ends up by using the correct specialization in the end -- but | |
30 | // without this skeleton it doesn't recognize Result as a class at all below | |
31 | #if defined(__VISUALC__) && !wxCHECK_VISUALC_VERSION(7) | |
32 | { | |
33 | template<typename TTrue, typename TFalse> struct Result {}; | |
34 | } | |
35 | #endif // VC++ <= 6 | |
36 | ; | |
37 | ||
38 | // specialization for true: | |
39 | template <> | |
40 | struct wxIfImpl<true> | |
41 | { | |
42 | template<typename TTrue, typename TFalse> struct Result | |
43 | { | |
44 | typedef TTrue value; | |
45 | }; | |
46 | }; | |
47 | ||
48 | // specialization for false: | |
49 | template<> | |
50 | struct wxIfImpl<false> | |
51 | { | |
52 | template<typename TTrue, typename TFalse> struct Result | |
53 | { | |
54 | typedef TFalse value; | |
55 | }; | |
56 | }; | |
57 | ||
58 | } // namespace wxPrivate | |
59 | ||
60 | // wxIf<> template defines nested type "value" which is the same as | |
61 | // TTrue if the condition Cond (boolean compile-time constant) was met and | |
62 | // TFalse if it wasn't. | |
63 | // | |
64 | // See wxVector<T> in vector.h for usage example | |
65 | template<bool Cond, typename TTrue, typename TFalse> | |
66 | struct wxIf | |
67 | { | |
68 | typedef typename wxPrivate::wxIfImpl<Cond> | |
69 | ::template Result<TTrue, TFalse>::value | |
70 | value; | |
71 | }; | |
72 | ||
73 | #endif // _WX_META_IF_H_ |