Hi Dave,
For myClassA, you will always have to cast the return value to myClassB
if you know that’s what will be returned. For a great blog post on the subject,
I give you Mike Ash:
https://mikeash.com/pyblog/friday-qa-2015-11-20-covariance-and-contravariance.html
Jeff Kelley
slauncha...@gmail.com | @SlaunchaMan <https://twitter.com/SlaunchaMan> |
jeffkelley.org <http://jeffkelley.org/>
> On Jan 4, 2016, at 11:24 AM, Dave <d...@looktowindward.com> wrote:
>
> Hi,
>
> In Objective-C, is it possible to override a property and have it return a
> different type to the base class?
>
> I have a base class with the following property defined:
>
> @property (nonatomic,retain) ClassA* propA;
>
> and the following getter:
>
>
> -(ClassA*) propA
> {
> return someValueOfClassA;
> }
>
>
> I’d like to override this in my subclass, as so:
>
> -(ClassB*) propA
> {
> ClassA* myClassA;
> ClassB* myClassB;
>
> myClassA = super.propA;
> myClassB = [[ClassB alloc] initWithClassA:myClassA]; //ClassB is a subclass
> of Class A
>
> return myClassB;
> }
>
> I can do this ok, but when I access the property:
>
> // myClassA is already setup OK
> ClassB* myClassB;
>
> myClassB = myClassA.propA; //Warning on this line saying
> return type is not ClassB
>
> and I have to coerce the value to be ClassB to get rid of the warning. Is
> there any way to avoid this?
>
> Thanks a lot
> Dave
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