Question

Is there ability to insert base class to inheritance hierarchy?
Here is an example:

@interface BaseClass // has a lot of basic functionality and interface
{...}
@end

@interface ChildClass : BaseClass // customizes BaseClass functionality
{...}
@end

@interface BaseClassEx : BaseClass // add some features to base class
{...}
@end

I want to have ChildClassEx that has all methods from ChildClass but is inherited from BaseClassEx

Answer 1

Sounds like multiple inheritance. Objective C doesn’t have it.

Based on your description, I would suggest a different design pattern.

@class BaseUtility // has a lot of basic functionality
{...}
@end

@class BaseClass // has interface
{...}
@property BaseUtility *utility;
@end

@class ChildUtility : BaseUtility // customizes basic functionality
{...}
@end

@class BaseClassEx : BaseClass // add some features to base class
{...}
@end

Now you can have four kinds of things.

1. A BaseClass with a BaseUtility assigned to it, which is like your BaseClass.
2. A BaseClass with a ChildUtility assigned to it, which is like your ChildClass. It gets customized behavior and has the same interface as BaseClass.
3. A BaseClassEx with a BaseUtility assigned to it, which is like your BaseClassEx. It has extra features (extra interface I assume).
4. A BaseClassEx with a ChildUtility assigned to it, which is like the ChildClassEx that you want. It has extra features and customized functionality.

Class inheritance is the “is a” pattern. The above combines both the “is a” pattern and the “has a” pattern. To get the effect of a ChildClassEx you want, you make something that “is a” BaseClassEx, but “has a” ChildUtility.