Objective C - Can't set superclass property in subclass - objective-c

Question

Take this simple class hierarchy:
Tree.h:
#interface Tree : NSObject
#property (nonatomic, assign) id<TreeDelegate> delegate;
#end
Tree.m:
#implementation Tree
#synthesize delegate;
#end
Aspen.h:
#interface Aspen : Tree
- (void)grow:(id<TreeDelegate>)delegate;
#end
Aspen.m:
#implementation Aspen
- (void) grow:(id<TreeDelegate>)d {
self.delegate = d;
}
#end
When I try to do self.delegate = d;, I'm getting the following error:
-[Aspen setDelegate:]: unrecognized selector sent to instance 0x586da00
I was expecting the Tree parent class's delegate property to be visible to the subclass as-is, but it doesn't seem to be since the error indicates the parent class's synthesized setter isn't visible.
What am I missing? Do I have to redeclare the property at the subclass level? I tried adding #dynamic at the top of the implementation of Aspen but that didn't work either. Such a simple concept here, but I've lost an hour searching around trying to find a solution. Out of ideas at this point.
--EDIT--
The above code is just a very stripped-down example to demonstrate the issue I'm seeing.

Answer 1

I just tried your code, supplemented by the protocol, an object implementing it, the necessary import and a main function and on my system it works like a charm:
#import <Foundation/Foundation.h>
#protocol TreeDelegate <NSObject>
#end
#interface MyDelegate : NSObject <TreeDelegate>
#end
#implementation MyDelegate
#end
#interface Tree : NSObject
#property (nonatomic, assign) id<TreeDelegate> delegate;
#end
#interface Aspen : Tree
- (void)grow:(id<TreeDelegate>)delegate;
#end
#implementation Tree
#synthesize delegate;
#end
#implementation Aspen
- (void) grow:(id<TreeDelegate>)d {
self.delegate = d;
}
#end
int main(int argc, char ** argv) {
MyDelegate * d = [[MyDelegate alloc] init];
Aspen * a = [[Aspen alloc] init];
[a grow:d];
return 0;
}

Answer 2

I was finally able to figure this out. My actual code leverages a 3rd party static library that defines the classes Tree and Aspen in my example. I had built a new version of the static library that exposed the Tree delegate given in my example, however I did not properly re-link the library after adding it to my project and as a result the old version was still being accessed at runtime.
Lessons learned: be diligent with steps to import a 3rd party library, and when simple fundamental programming concepts (such as in my example text) aren't working, take a step back and make sure you've dotted i's and crossed t's.