docs/doxygen/overviews/cpprttidisabled.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        cpprttidisabled.h
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // Licence:     wxWindows licence
   6 /////////////////////////////////////////////////////////////////////////////
   7
   8 /**
   9
  10 @page overview_cpp_rtti_disabled Caveats When Not Using C++ RTTI
  11
  12 @tableofcontents
  13
  14 @note C++ RTTI is usually enabled by default in most wxWidgets builds. If you
  15       do not know if your build has C++ RTTI enabled or not, then it probably
  16       is enabled, and you should not worry about anything mentioned in this
  17       section.
  18
  19 While in general wxWidgets standard @ref overview_rtti is used throughout the
  20 library, there are some places where it won't work. One of those places
  21 is template classes.
  22
  23 When available, C++ RTTI is used to address this issue. If you have built the
  24 library with C++ RTTI disabled, an internal RTTI system is substituted.
  25 However, this system is not perfect and one proven scenario where it may break
  26 is a shared library or DLL build. More specifically, a template class instance
  27 created in one physical binary may not be recognized as its correct type when
  28 used in another one.
  29
  30 @see @ref overview_rtti, wxEvtHandler::Bind(), wxAny
  31
  32
  33
  34 @section overview_cpp_rtti_disabled_bind Bind() Issues
  35
  36 wxWidgets 2.9.0 introduced a new @ref overview_events_bind system, using
  37 wxEvtHandler::Bind<>() and Unbind<>(). This functionality uses templates
  38 behind the scenes and therefore is vulnerable to breakage in shared library
  39 builds, as described above.
  40
  41 Currently only Unbind<>() needs the type information, so you should be immune
  42 to this problem simply if you only need to use Bind<>() and not Unbind<>().
  43
  44 Also, if you only bind and unbind same event handler inside same binary, you
  45 should be fine.
  46
  47
  48
  49 @section overview_cpp_rtti_disabled_wxany wxAny Issues
  50
  51 wxAny is a dynamic type class which transparently uses templates to generate
  52 data type handlers, and therefore is vulnerable to breakage in shared library
  53 builds, as described above
  54
  55 You should be fine if you only create and use wxAny instances inside same
  56 physical binary. However, if you do need to be able to use wxAny freely
  57 across binary boundaries, (and for sake of code-safety, you probably do),
  58 then specializations for wxAnyValueTypeImpl<> templates need to be defined in
  59 one of your shared library (DLL) files. One specialization is required for
  60 every data type you use with wxAny. Easiest way to do this is using macros
  61 provided in wx/any.h. Note that you @b do @b not need to define
  62 specializations for C built-in types, nor for wxString or wxDateTime, because
  63 these are already provided in wxBase. However, you @b do need to define
  64 specializations for all pointer types except char* and wchar_t*.
  65
  66 Let's define a specialization for imaginary type 'MyClass'. In your shared
  67 library source code you will need to have this line:
  68
  69 @code
  70     WX_IMPLEMENT_ANY_VALUE_TYPE(wxAnyValueTypeImpl<MyClass>)
  71 @endcode
  72
  73 In your header file you will need the following:
  74
  75 @code
  76     wxDECLARE_ANY_TYPE(MyClass, WXIMPORT_OR_WXEXPORT)
  77 @endcode
  78
  79 Where WXIMPORT_OR_WXEXPORT is WXEXPORT when being included from the shared
  80 library that called the WX_IMPLEMENT_ANY_VALUE_TYPE() macro, and WXIMPORT
  81 otherwise.
  82
  83 */