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