[Axl] CHANGE-NOTIFICATION: axl-bool-removal-02

[Francis Brosnan Blazquez]

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    Change Id: axl-bool-removal-02
     Replaces: axl-bool-removal-01 [6]
 Project name: Axl library
  Included in: 0.5.5
       Status: NOTIFY
       Author: Francis Brosnan Blázquez

Motivation
~~~~~~~~~~

Previous change notification (axl-bool-removal-01 [6]) did not fully
solve the problem that motivated the change. This is because compiling
Axl Library with a C++/C99 tool, may lead to having unexpected results
with internal false and true values used by the library (and allowed
by previous change notification).

The modification presented in this change notification will cover
these issues and will provide a way to applications already deployed
with bool/false/true imported by Axl Library to still work.

Change Description
~~~~~~~~~~~~~~~~~~

The following is not only the change description but also the way
boolean types are used in Axl Library.

1) For the internal Axl Library use, its components, tools and
   regression test, the boolean type will be modeled as:
  
   - axl_bool (which is a type definition to int)

   - axl_false (which represents the boolean false state). This value
     replaces deprecated "false" declaration.

   - axl_true  (which represents the boolean true state). This value
     replaces deprecated "true" declaration.

2) It is recommend that applications and libraries using Axl Library
   API to use these definitions and to avoid using bool/false/true.

3) For C users that do not define __axl_disable_broken_bool_def__, the
   old boolean definition is still available, that is: bool/false/true
   as they were defined in previous releases.

4) All functions receiving or returning bool values now receive or
   return axl_bool

Solution to incompatibility
~~~~~~~~~~~~~~~~~~~~~~~~~~~

C users:   using Axl Library with no problem until now will have no
~~~~~~~~   effect. Its code will still compile and run properly
           without modification. The API is also binary compatible.

           For these users it is also provided a compiler directive
           which disables actual boolean definition, which is
           considered problematic. gcc users may use:

           -D__axl_disable_broken_bool_def

           In many cases this is not necessary. However, it is
           recommended it you are building a library on top of Axl or
           a product that may be used from C++ users or different C
           compilers.

c++ users: they won't need to use wrappers around functions using bool
~~~~~~~~~~ type from Axl Library for newly written code. For wrappers
           already written, they will still work since the Axl Library
           API is expecting int as in previous releases.

           This change notification revision improves previous one by
           allowing C++/C users to use axl_bool type and its static
           values axl_false and axl_true with no problem.

References
~~~~~~~~~~
[1] Axl library
    http://xml.aspl.es

[2] Axl library change notifications
    http://xml.aspl.es/doc.html

[3] Change notification definition
    http://www.aspl.es/change/change-notification.txt

[4] A discussion about int and bool type on Axl and Vortex API
    http://lists.aspl.es/pipermail/vortex/2008-October/000712.html

[5] An article about integer types
    http://home.att.net/~jackklein/c/inttypes.html

[6] http://lists.aspl.es/pipermail/axl/2008-October/000093.html


-- 
Francis Brosnan Blazquez <francis at aspl.es>
Advanced Software Production Line, S.L.