OOP Using GObject (4) – An Inheritable Class

Now, we will begin to implement some real OO mechanism using GObject library. In this article, we will make our fundamental type Inheritable.

Here’s comes our Base type:

NOTE: PLEASE READ ALL COMMENT CAREFULLY.

In base_instance_init(), we assigned the base_instance_dump() callback. Thus, we can invoke this function by both global function or instance function of BaseClass class. Additional flags G_TYPE_FLAG_DERIVABLE and G_TYPE_FLAG_DEEP_DERIVABLE are also passed to the GTypeFundamentalInfo struct to enable inheritance.

It’s time to define our Derived type:

Our Derived type inherits Base by replacing GTypeClass and GTypeInstance with the corresponding struct of the Base type. According to the memory layout of structs, GTypeClass and GTypeInstance are still the first member of corresponding struct. In derived_get_type(), we register Derived type using g_type_register_static() since it’s not a fundamental at all. And the first parameter is the type id of Base type.

Let’s have some time to look up how to implement polymorphism. In derived_class_init(), we re-assign the base_instance_dump() callback to from the Base‘s implementation to Derived‘s implementation.

Test code:

All source code is available in my skydrive: http://cid-481cbe104492a3af.office.live.com/browse.aspx/share/dev/TestOO. In the TestGObject-{date}.zip/TestGObject4 folder.

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