docs/doxygen/overviews/cpprttidisabled.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        cpprttidisabled.h
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows licence
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10
  11 @page overview_cpp_rtti_disabled Caveats When Not Using C++ RTTI
  12
  13 @tableofcontents
  14
  15 @note C++ RTTI is usually enabled by default in most wxWidgets builds. If you
  16       do not know if your build has C++ RTTI enabled or not, then it probably
  17       is enabled, and you should not worry about anything mentioned in this
  18       section.
  19
  20 While in general wxWidgets standard @ref overview_rtti is used throughout the
  21 library, there are some places where it won't work. One of those places
  22 is template classes.
  23
  24 When available, C++ RTTI is used to address this issue. If you have built the
  25 library with C++ RTTI disabled, an internal RTTI system is substituted.
  26 However, this system is not perfect and one proven scenario where it may break
  27 is a shared library or DLL build. More specifically, a template class instance
  28 created in one physical binary may not be recognized as its correct type when
  29 used in another one.
  30
  31 @see @ref overview_rtti, wxEvtHandler::Bind(), wxAny
  32
  33
  34
  35 @section overview_cpp_rtti_disabled_bind Bind() Issues
  36
  37 wxWidgets 2.9.0 introduced a new @ref overview_events_bind system, using
  38 wxEvtHandler::Bind<>() and Unbind<>(). This functionality uses templates
  39 behind the scenes and therefore is vulnerable to breakage in shared library
  40 builds, as described above.
  41
  42 Currently only Unbind<>() needs the type information, so you should be immune
  43 to this problem simply if you only need to use Bind<>() and not Unbind<>().
  44
  45 Also, if you only bind and unbind same event handler inside same binary, you
  46 should be fine.
  47
  48
  49
  50 @section overview_cpp_rtti_disabled_wxany wxAny Issues
  51
  52 wxAny is a dynamic type class which transparently uses templates to generate
  53 data type handlers, and therefore is vulnerable to breakage in shared library
  54 builds, as described above
  55
  56 You should be fine if you only create and use wxAny instances inside same
  57 physical binary. However, if you do need to be able to use wxAny freely
  58 across binary boundaries, (and for sake of code-safety, you probably do),
  59 then specializations for wxAnyValueTypeImpl<> templates need to be defined in
  60 one of your shared library (DLL) files. One specialization is required for
  61 every data type you use with wxAny. Easiest way to do this is using macros
  62 provided in wx/any.h. Note that you @b do @b not need to define
  63 specializations for C built-in types, nor for wxString or wxDateTime, because
  64 these are already provided in wxBase. However, you @b do need to define
  65 specializations for all pointer types except char* and wchar_t*.
  66
  67 Let's define a specialization for imaginary type 'MyClass'. In your shared
  68 library source code you will need to have this line:
  69
  70 @code
  71     WX_IMPLEMENT_ANY_VALUE_TYPE(wxAnyValueTypeImpl<MyClass>)
  72 @endcode
  73
  74 In your header file you will need the following:
  75
  76 @code
  77     wxDECLARE_ANY_TYPE(MyClass, WXIMPORT_OR_WXEXPORT)
  78 @endcode
  79
  80 Where WXIMPORT_OR_WXEXPORT is WXEXPORT when being included from the shared
  81 library that called the WX_IMPLEMENT_ANY_VALUE_TYPE() macro, and WXIMPORT
  82 otherwise.
  83
  84 */