Resolve ambiguity between GetClientXXX() methods in wxOSX wxComboBox.

[wxWidgets.git] / docs / tech / tn0020.txt

diff --git a/docs/tech/tn0020.txt b/docs/tech/tn0020.txt
index d351b4e349e2608c3996d82ec60d5847c6b415f3..e83c319a6206e201aa80ae1f30e76c1042179d84 100644 (file)
--- a/docs/tech/tn0020.txt
+++ b/docs/tech/tn0020.txt
@@ -3,13 +3,13 @@
 0. Purpose
 ----------
 
 0. Purpose
 ----------
 

-This is broad technote covering all aspects of binary compatibility with 
+This is a broad technote covering all aspects of binary compatibility with

 wxWidgets.
 
 1. Releases
 -----------
 
 wxWidgets.
 
 1. Releases
 -----------
 

-General overview of releases can be found in tn0012.txt, but for 
+General overview of releases can be found in tn0012.txt, but for

 completeness the wxWidgets release version number is as follows:
 
 2.6.2
 completeness the wxWidgets release version number is as follows:
 
 2.6.2


@@ -37,17 +37,23 @@ also section (4).
 -------------------------------------------------
 
 If its still up, the KDE guide is a good reference:
 -------------------------------------------------
 
 If its still up, the KDE guide is a good reference:

-http://developer.kde.org/documentation/other/binarycompatibility.html
+http://techbase.kde.org/Policies/Binary_Compatibility_Issues_With_C++

 
 The changes that are NOT binary compatible:
 - Adding a virtual function
 - Changing the name of a any function or variable
 
 The changes that are NOT binary compatible:
 - Adding a virtual function
 - Changing the name of a any function or variable

-- Changing the signature of a virtual function (adding a parameter, 
+- Changing the signature of a virtual function (adding a parameter,

 even a default one)
 - Changing the order of the virtual functions in a class
 ["switching" them, etc.]
 even a default one)
 - Changing the order of the virtual functions in a class
 ["switching" them, etc.]

-- Changing access privileges to a function (protected to private etc.)
-[unlike KDE we need to support windows so this is not allowed]
+- Changing access privileges of a function: some compilers (among which MSVC)
+  use the function access specifier in its mangled name. Moreover, while
+  changing a private function to public should be compatible (as the old
+  symbol can't be referenced from outside the library anyhow), changing a
+  virtual private function to public is NOT compatible because the old symbol
+  is referenced by the virtual tables in the executable code and so an old
+  program compiled with MSVC wouldn't start up with a new DLL even if it
+  doesn't use the affected symbol at all!

 - Adding a member variable
 - Changing the order of non-static member variables
 
 - Adding a member variable
 - Changing the order of non-static member variables
 


@@ -57,6 +63,7 @@ even a default one)
 
 - Adding a new class
 - Adding a new non-virtual method to an existing class
 
 - Adding a new class
 - Adding a new non-virtual method to an existing class

+- Adding a new constructor to an existing class

 - Overriding the implementation of an existing virtual function
 [this is considered to be backwards binary compatible until we find a
  counter example; currently it's known to work with Apple gcc at least]
 - Overriding the implementation of an existing virtual function
 [this is considered to be backwards binary compatible until we find a
  counter example; currently it's known to work with Apple gcc at least]


@@ -107,7 +114,7 @@ bool    ShowPlayerControls(
 //helpers for the wxPython people
 bool LoadURI(const wxString& fileName)
 {   return Load(wxURI(fileName));       }
 //helpers for the wxPython people
 bool LoadURI(const wxString& fileName)
 {   return Load(wxURI(fileName));       }

-bool LoadURIWithProxy(const wxString& fileName, const wxString& proxy)     
+bool LoadURIWithProxy(const wxString& fileName, const wxString& proxy)

 {   return Load(wxURI(fileName), wxURI(proxy));       }
 #endif
 
 {   return Load(wxURI(fileName), wxURI(proxy));       }
 #endif
 


@@ -133,7 +140,7 @@ wxShadowObject resides in include/wx/clntdata.h.
 
 To use wxShadowObject, you first call AddMethod or AddField with
 the first parameter being the name of the field and/or method
 
 To use wxShadowObject, you first call AddMethod or AddField with
 the first parameter being the name of the field and/or method

-you want, and the second parameter being the value of the 
+you want, and the second parameter being the value of the

 field and/or method.
 
 In the case of fields this is a void*, and in the case of method
 field and/or method.
 
 In the case of fields this is a void*, and in the case of method


@@ -144,15 +151,15 @@ After you add a field, you can set it via SetField with the same
 parameters as AddField, the second parameter being the value to set
 the field to.  You can get the field after you call AddField
 via GetField, with the parameters as the other two field functions,
 parameters as AddField, the second parameter being the value to set
 the field to.  You can get the field after you call AddField
 via GetField, with the parameters as the other two field functions,

-only in the case the second parameter is the fallback 
-value for the field in the case of it not being found in the 
-hash map.  
+only in the case the second parameter is the fallback
+value for the field in the case of it not being found in the
+hash map.

 
 You can call a method after you add it via InvokeMethod, which
 returns a bool indicating whether or not the method was found
 in the hash map, and has 4 parameters.  The first parameter is
 the name of the method you wish to call, the second is the first
 
 You can call a method after you add it via InvokeMethod, which
 returns a bool indicating whether or not the method was found
 in the hash map, and has 4 parameters.  The first parameter is
 the name of the method you wish to call, the second is the first

-parameter passed to the wxShadowObjectMethod, the third is the 
+parameter passed to the wxShadowObjectMethod, the third is the

 second parameter passed to that wxShadowObjectMethod, and the
 fourth is the return value of the wxShadowObjectMethod.
 
 second parameter passed to that wxShadowObjectMethod, and the
 fourth is the return value of the wxShadowObjectMethod.
 


@@ -177,7 +184,7 @@ The file has the layout as follows:
 Where X is the current Release as mentioned earlier, i.e. 2.  This
 is following by an opening bracket "{", followed by "global:",
 followed by patterns matching added symbols, then followed by "}", and then
 Where X is the current Release as mentioned earlier, i.e. 2.  This
 is following by an opening bracket "{", followed by "global:",
 followed by patterns matching added symbols, then followed by "}", and then

-the file is either followed by earlier Releases or ended by 
+the file is either followed by earlier Releases or ended by

 a @WX_VERSION_TAG@ block without the period or Release.
 
 The patterns used to specify added symbols are globbing patters and can
 a @WX_VERSION_TAG@ block without the period or Release.
 
 The patterns used to specify added symbols are globbing patters and can


@@ -264,10 +271,15 @@ binary compatibility between those releases.
 You can also break into your debugger or whatever program you want
 to use and check the memory layout of the class.  If it is the same
 then it is binary compatible.
 You can also break into your debugger or whatever program you want
 to use and check the memory layout of the class.  If it is the same
 then it is binary compatible.

-
-Also remember to look at http://www.wxwidgets.org/bincompat.html page which
-summarizes the results of testing of all the samples built against old
-libraries headers with the new library binaries under Unix.
+(In GDB the command x/d will show addresses as pointers to functions if
+possible so you can see if the order of the functions in vtbl doesn't change.)
+
+Another way to check for binary compatibility is to build wxWidgets in shared mode
+and use the 'abicheck.sh --generate' script before doing your changes to generate
+the current ABI (if the 'expected_abi' file is not already in the repo).
+Then rebuild wxWidgets with your changes and use 'abicheck.sh' to compare the
+resulting ABI with the expected one.
+Note that the abicheck.sh script is in the "lib" folder.

 
 
 === EOF ===
 
 
 === EOF ===