include/wx/meta/if.h

   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 // NB: This code is intentionally written without partial templates
  15 //     specialization, because some older compilers (notably VC6) don't
  16 //     support it.
  17
  18 namespace wxPrivate
  19 {
  20
  21 template<bool Cond> struct wxIfImpl {};
  22
  23 // specialization for true:
  24 template<>
  25 struct wxIfImpl<true>
  26 {
  27     template<typename TTrue, typename TFalse> struct Result
  28     {
  29         typedef TTrue value;
  30     };
  31 };
  32
  33 // specialization for false:
  34 template<>
  35 struct wxIfImpl<false>
  36 {
  37     template<typename TTrue, typename TFalse> struct Result
  38     {
  39         typedef TFalse value;
  40     };
  41 };
  42
  43 } // namespace wxPrivate
  44
  45 // wxIf<> template defines nested type "value" which is the same as
  46 // TTrue if the condition Cond (boolean compile-time constant) was met and
  47 // TFalse if it wasn't.
  48 //
  49 // See wxVector<T> in vector.h for usage example
  50 template<bool Cond, typename TTrue, typename TFalse>
  51 struct wxIf
  52 {
  53     typedef typename wxPrivate::wxIfImpl<Cond>
  54                          ::template Result<TTrue,TFalse>::value
  55             value;
  56 };
  57
  58 #endif // _WX_META_IF_H_