Ghostvars cross-linking code-generation possibilities: - RJL051121
RJLRef: $PH/COOL-BDE/bdegencpp/gencpp_ghostvars.051121.txt

I am resurrecting the ghostvars project, motivated by 
RAlmonte's 05f523 reference to the OpenSource project 
libpropc++ at http://ex-code.com/propcpp/: 

The libpropc++ library supports cross-notification 
[and cross-update?] between two [or more?] sources 
of object data changes (see appended extract).

[Update 060212: the uSoft SWFactories text (06s524)
 says transformations that can map one level of abstraction
 to another are a 'critical innovation' 
 for SW industrialization.]
-----------------------------------

libpropc++ claims inspired me to create a related set 
of notes in $PH/COOL-BDE/bdegencpp/aareadme,
(linked from $PH/05f523/week12/aareadme_bdegencpp).

That aareadme discusses a concept for auto-generating 
code for cross-linking and updating 'ghost' variables 
in class data members.  [Ref: $PH/ghostvarsRev3]

I conjecture that this code can be auto-generated 
by gencpp, after adding 1-to-1 associative entities 
and new cross-mapping access macros to pr_accessors.c 
and recompiling pr_util, without changing any code 
in the two classes it couples. Code changes would be
confined to the XXSetField access methods and 
compiled conditionally like logging is.

[Any volunteers for a new MS thesis on 
auto-generating code for ghostvar maintenance?
(Prachee Sharma did one circa 2000).]


aareadme_bdegencpp also proposes adding four other new 
groups of table types to bde's schema.sch file, 
oriented toward a LCP-style MVController. 
These would be invisible at first
without requiring bde code changes
(First goal is to get bde to compile with gencpp.)

===========================================
Extract from libpropc++ homepage http://ex-code.com/propcpp/:

> This is libpropc++ 1.0 library - the ANSI C++ template library
> to create "properties" of objects:
>
> Property<Widget, Color,
>          &Widget::set_color, &Widget::get_color> color;
>  which can be manipulated like this:
>
> widget.color = "red";
> Properties can be bound with other properties to automatically synchronize
their values (so that when one property changes, the other changes
accordingly). libpropc++ supports many different kinds of binding properties
including one-directional and two-directional bindings, bindings properties
of different value types and binding with a value transformation (by a
function or an other kind of functor).
 
-------------------------------------

> See this article for detailed discussions about binding properties in general.
> Binding properties particularly simplifies development of GUI applications:
> checkbox.checked.bind(frame.visible);
> mutual_bind(menu_item.selected, appPrefs.configItem);
> libpropc++ also has built-in signalling (Observer Pattern from object
oriented methodology) implementation or (alternatively) can use libsigc++
for signalling. Signal programming is the programming paradigm of an object
notifying other objects when some event (for example change of a value of a
property) happens.
>
> libpropc++ API is documented using Doxygen.
>
> libpropc++ is written using highest programming technologies and standards
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