include/wx/meta/implicitconversion.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        wx/meta/implicitconversion.h
   3 // Purpose:     Determine resulting type from implicit conversion
   4 // Author:      Vaclav Slavik
   5 // Created:     2010-10-22
   6 // RCS-ID:      $Id$
   7 // Copyright:   (c) 2010 Vaclav Slavik
   8 // Licence:     wxWindows licence
   9 /////////////////////////////////////////////////////////////////////////////
  10
  11 #ifndef _WX_META_IMPLICITCONVERSION_H_
  12 #define _WX_META_IMPLICITCONVERSION_H_
  13
  14 #include "wx/defs.h"
  15 #include "wx/meta/if.h"
  16
  17 // C++ hierarchy of data types is:
  18 //
  19 //   Long double (highest)
  20 //   Double
  21 //   Float
  22 //   Unsigned long int
  23 //   Long int
  24 //   Unsigned int
  25 //   Int (lowest)
  26 //
  27 // Types lower in the hierarchy are converted into ones higher up if both are
  28 // involved e.g. in arithmetic expressions.
  29
  30 namespace wxPrivate
  31 {
  32
  33 // Helper macro to define a constant inside a template class: it's needed
  34 // because MSVC6 doesn't support initializing static integer members but the
  35 // usual workaround of using enums instead doesn't work for Borland (at least
  36 // in template classes).
  37 #ifdef __VISUALC6__
  38     #define wxDEFINE_CLASS_INT_CONST(name, value) enum { name = value }
  39 #else
  40     #define wxDEFINE_CLASS_INT_CONST(name, value) static const int name = value
  41 #endif
  42
  43 template<typename T>
  44 struct TypeHierarchy
  45 {
  46     // consider unknown types (e.g. objects, pointers) to be of highest
  47     // level, always convert to them if they occur
  48     wxDEFINE_CLASS_INT_CONST( level, 9999 );
  49 };
  50
  51 #define WX_TYPE_HIERARCHY_LEVEL(level_num, type)        \
  52     template<> struct TypeHierarchy<type>               \
  53     {                                                   \
  54         wxDEFINE_CLASS_INT_CONST( level, level_num );   \
  55     }
  56
  57 WX_TYPE_HIERARCHY_LEVEL( 1, char);
  58 WX_TYPE_HIERARCHY_LEVEL( 2, unsigned char);
  59 WX_TYPE_HIERARCHY_LEVEL( 3, short);
  60 WX_TYPE_HIERARCHY_LEVEL( 4, unsigned short);
  61 WX_TYPE_HIERARCHY_LEVEL( 5, int);
  62 WX_TYPE_HIERARCHY_LEVEL( 6, unsigned int);
  63 WX_TYPE_HIERARCHY_LEVEL( 7, long);
  64 WX_TYPE_HIERARCHY_LEVEL( 8, unsigned long);
  65 #ifdef wxLongLong_t
  66 WX_TYPE_HIERARCHY_LEVEL( 9, wxLongLong_t);
  67 WX_TYPE_HIERARCHY_LEVEL(10, wxULongLong_t);
  68 #endif
  69 WX_TYPE_HIERARCHY_LEVEL(11, float);
  70 WX_TYPE_HIERARCHY_LEVEL(12, double);
  71 WX_TYPE_HIERARCHY_LEVEL(13, long double);
  72
  73 #if wxWCHAR_T_IS_REAL_TYPE
  74     #if SIZEOF_WCHAR_T == SIZEOF_SHORT
  75       template<> struct TypeHierarchy<wchar_t> : public TypeHierarchy<short> {};
  76     #elif SIZEOF_WCHAR_T == SIZEOF_INT
  77       template<> struct TypeHierarchy<wchar_t> : public TypeHierarchy<int> {};
  78     #elif SIZEOF_WCHAR_T == SIZEOF_LONG
  79       template<> struct TypeHierarchy<wchar_t> : public TypeHierarchy<long> {};
  80     #else
  81       #error "weird wchar_t size, please update this code"
  82     #endif
  83 #endif
  84
  85 #undef WX_TYPE_HIERARCHY_LEVEL
  86
  87 } // namespace wxPrivate
  88
  89 // Helper to determine resulting type of implicit conversion in
  90 // an expression with two arithmetic types.
  91 template<typename T1, typename T2>
  92 struct wxImplicitConversionType
  93 {
  94     typedef typename wxIf
  95             <
  96                 // if T2 is "higher" type, convert to it
  97                 (int)(wxPrivate::TypeHierarchy<T1>::level) < (int)(wxPrivate::TypeHierarchy<T2>::level),
  98                 T2,
  99                 // otherwise use T1
 100                 T1
 101             >::value
 102             value;
 103 };
 104
 105
 106 template<typename T1, typename T2, typename T3>
 107 struct wxImplicitConversionType3 : public wxImplicitConversionType<
 108                         T1,
 109                         typename wxImplicitConversionType<T2,T3>::value>
 110 {
 111 };
 112
 113 #endif // _WX_META_IMPLICITCONVERSION_H_