GObject in GC implementation Plan

[Daniel Espinosa]

GOBJECT IN GC IMPLEMENTATION PLAN:

OBJECTIVE

Get GObject as the base of GC's objects. With the following advantages:
	- Get ref counting
	- Get signals events



STATE OF THE ART

QOF is the object system used by the GC's objects, it has the
following features:
	- Base class Object construction/destruction
	- Signal handling
	- Type system based on strings
	- Objects Properties like system called Parameters

GC's objects depends directly from QofInstance, witch actually depends
directly from QofEntity, both QofInstance and QofEntity, are virtual
objects that means you can't create an instance of them; then the GC's
objects when created need to init its base class QofInstance and this
its own QofEntity.

QofEntity holds the GUID, the unique id for the object, the type of
the object as a string and a pointer to the QofCollection where this
entity is stored.

QofInstance holds pointer to the book it belongs to, and information
that allows to know the state of the object related to commit to the
backend.

The string type system is hard to change for now, then this will need
be modified in other work; for now is possible to leave it as is,
because changing to GType means to alter the way of QofBook stores
objects, QofParam identifies the parameters types, and QofQuery
identifies the parameters.



STEPS TO GET GOBJECT

In order to get GObject as the base class for the GC's objects and get
its functionalities, we can go though the following options:




******OPTION 1: PORT QofEntity TO USE GObject AS BASE CLASS

Step 1:
Setup QofEntity, QofInstance and ALL GC's objects to be GObjects in
order to have a correct construction/destruction process, this will
ensure a correct refcounting.

**ADVANTAGES
Make all in one step and get GObject from the base QOF system.

**DISADVANTAGES
Too many changes to be mergable in Trunk.





*******OPTION 2: PORT QofInstance TO USE GObject AS BASE CLASS

Step 1:
Merge QofInstance and QofEntity. This allow to get a single class used
as the base for the GC's objects.

Step 2:
Setup QofInstance and ALL GC's objects to be GObjects and be sure to
have a correct construction/destruction process, this will ensure a
correct refcounting.

**ADVANTAGES
Make all in few steps and get GObject from the base QOF system.
Simplify the object class hierarchy.

**DISADVANTAGES
Too many changes to be mergable in Trunk.




*******OPTION 3: PORT GC's OBJECT TO USE GObject AS BASE CLASS

Step 1: (this step can be done Object by Object, don't need to work in
all objects at the same time)
Make the QofInstance member as a Pointer, and allow to create a
pointer to a QofInstance when the object is created using
g_object_new. This means:

	- Add a new function in QofInstance to allow create an instance,
setup it and return a pointer to a QofInstance
	- No modification in the current QofInstance implementation
	- Will need to change all references (JUST in the currently changing
object) from 'object->inst.[someQofInstanceMember]' to
'object->inst->[someQofInstanceMember]'
	- Needs to change the definition of QOF_INSTANCE macro to call a
functions witch returns the QofInstance pointer member of the GC's
object

Step 2:
Setup the currently working object to be a GObject. This means:
	- The base class will be GObject not QofInstance
	- Other objects, not currently changing, will use the same
QofInstance base class and its current construction/destruction
process

Step 3:
Merge QofInstance and QofEntity. This allow to get a single base class.

Step 4:
Setup QofInstance to be a GObject and be sure to have a correct
construction/destruction process, this will ensure a correct
refcounting.

Step 5:
Now we can change the base class from GObject to QofInstance in all
GC's objects.

**ADVANTAGES
Get GObject features directly in GC's objects quickly.
Allows to delay the required modifications in QOF to later steps.
Allows to modify QOF WITH OUT modify the GC's objects; even is
possible to work on QOF with out modify the GC's objects, but this
delay to get GObject in GC
Once the process in QOF to GObject is finished we can change the base
class in GC's objects again to QofInstance
Simplify the object class hierarchy.

**DISADVANTAGES
Require to change the base class of the GC's objects from QofInstance
to GObject.
Needs to change the code from direct access to the members in
QofInstance from '.' to '->'.

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