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 @see @ref overview_rtti, wxEvtHandler::Bind(), wxAny
  16
  17
  18
  19 @section overview_cpp_rtti_disabled_intro Introduction
  20
  21 @note C++ RTTI is usually enabled by default in most wxWidgets builds. If you
  22       do not know if your build has C++ RTTI enabled or not, then it probably
  23       is enabled, and you should not worry about anything mentioned in this
  24       section.
  25
  26 While in general wxWidgets standard @ref overview_rtti is used throughout the
  27 library, there are some places where it won't work. One of those places
  28 is template classes.
  29
  30 When available, C++ RTTI is used to address this issue. If you have built the
  31 library with C++ RTTI disabled, an internal RTTI system is substituted.
  32 However, this system is not perfect and one proven scenario where it may break
  33 is a shared library or DLL build. More specifically, a template class instance
  34 created in one physical binary may not be recognized as its correct type when
  35 used in another one.
  36
  37
  38
  39 @section overview_cpp_rtti_disabled_bind Bind() Issues
  40
  41 wxWidgets 2.9.0 introduced a new @ref overview_events_bind system, using
  42 wxEvtHandler::Bind<>() and Unbind<>(). This functionality uses templates
  43 behind the scenes and therefore is vulnerable to breakage in shared library
  44 builds, as described above.
  45
  46 Currently only Unbind<>() needs the type information, so you should be immune
  47 to this problem simply if you only need to use Bind<>() and not Unbind<>().
  48
  49 Also, if you only bind and unbind same event handler inside same binary, you
  50 should be fine.
  51
  52
  53
  54 @section overview_cpp_rtti_disabled_wxany wxAny Issues
  55
  56 wxAny is a dynamic type class which transparently uses templates to generate
  57 data type handlers, and therefore is vulnerable to breakage in shared library
  58 builds, as described above
  59
  60 You should be fine if you only create and use wxAny instances inside same
  61 physical binary. However, if you do need to be able to use wxAny freely
  62 across binary boundaries, (and for sake of code-safety, you probably do),
  63 then specializations for wxAnyValueTypeImpl<> templates need to be defined in
  64 one of your shared library (DLL) files. One specialization is required for
  65 every data type you use with wxAny. Easiest way to do this is using macros
  66 provided in wx/any.h. Note that you @b do @b not need to define
  67 specializations for C built-in types, nor for wxString or wxDateTime, because
  68 these are already provided in wxBase. However, you @b do need to define
  69 specializations for all pointer types except char* and wchar_t*.
  70
  71 Let's define a specialization for imaginary type 'MyClass'. In your shared
  72 library source code you will need to have this line:
  73
  74 @code
  75     WX_IMPLEMENT_ANY_VALUE_TYPE(wxAnyValueTypeImpl<MyClass>)
  76 @endcode
  77
  78 In your header file you will need the following:
  79
  80 @code
  81     wxDECLARE_ANY_TYPE(MyClass, WXIMPORT_OR_WXEXPORT)
  82 @endcode
  83
  84 Where WXIMPORT_OR_WXEXPORT is WXEXPORT when being included from the shared
  85 library that called the WX_IMPLEMENT_ANY_VALUE_TYPE() macro, and WXIMPORT
  86 otherwise.
  87
  88 */