Question

I have a class called “BaseEntry” and some specific classes like “EntryFoo” and “EntryBar” which are subclasses from “Base Entry”.

Now there is a function getEntry which should return a Object which is subclass of BaseEntry. In Java this wouldn’t be a problem but I have no idea how to fix this in Objective-C for iOS.

Thanks for your help!
Alex

Answer 1

The standard way to do this in Objective-C is to just return an object of type ‘id’; think of it as Object in Java. However, id is slightly nicer in that you can assign the return value to a typed value without a cast.

To clarify, your options are:

// Assuming -(BaseEntry*)getEntry;
id entry = [obj getEntry];
[entry messageOnlyOnFooEntry];

// Assuming -(BaseEntry*)getEntry; - note cast required
FooEntry *entry = (FooEntry*)[obj getEntry];
[entry messageOnlyOnFooEntry];

// Assuming -(id)getEntry; - no cast required
FooEntry *entry = [obj getEntry];
[entry messageOnlyOnFooEntry];