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diff --git a/kdecore/KCONFIG_DESIGN b/kdecore/KCONFIG_DESIGN new file mode 100644 index 000000000..dfd9aa151 --- /dev/null +++ b/kdecore/KCONFIG_DESIGN @@ -0,0 +1,51 @@ + + The basic design on KConfig for KDE 2.0 and KDE 3.0: + ---------------------------------------- + +KConfig is a hierarchy of classes for loading and saving configuration +data in KDE. KConfigBase is an abstract data type (ADT) with pure +virtual functions which describes the API for accessing configuration +data. It cannot be instantiated directly; only subclasses which +actually implement the API may be created. The reason for this design +is that different ways of storing configuration data in _memory_ may +be desired. The default design uses a QMap (red-black tree) for +storing values in memory once they are read from disk. However, a +different design might use a shared database or something similar to +achieve shared memory config values. The possibilities are endless, +and with this design we insure that future designs will not break +compatibility. + +This means that most classes that currently take pointers to KConfig +objects should be changed to take pointers to KConfigBase objects. +The virtual functions and c++ polymorphism will make sure that the +correct function in the actual, instantiated object are called, but +this lets the user/programmer change the type of KConfig that has been +implemented at runtime without changing other code. + +Similarly, there is a abstract data type KConfigBackEnd. All +reading/writing of the physical, on-disk configuration should be done +through a subclass of KConfigBackEnd. The only class that is +currently implemented right now is KConfigINIBackEnd, which +reads/writes the standard windows INI-style configuration files that +KDE has used since KDE 1.x days. However, it is conceivable that one +might program an XML backend, or even a database/registry style +backend. Again, this abstract data type approach provides flexibility +for the future. Currently KConfig and KSimpleConfig hardcode that +they are using a KConfigINIBackEnd in the constructor. If more back +ends are implemented, this will have to be changed to use a factory +method of some sort to create the backend; all they maintain is a +pointer to a KConfigBackEnd, so the actual type of backend does not +matter. + +If you are interested in using KConfig, you need simply to look at the +public members of KConfigBase. They will provide you with everything +you need to do to look up data, change and write data, etc. If you +are interested in implementing a new KConfig format, look at KConfig +for ideas. Likewise if you want to implement a backend, look at +KConfigINIBackEnd for inspiration. The KDoc-style API documentation +should be complete. If there is anything confusing, please either fix +it in CVS yourself or mail me with your questions, and we will make +sure things get clarified. + + +- Preston Brown <pbrown@kde.org> |