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bdash/generics.m

Last active March 13, 2018 22:06
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Using Objective-C generics with type constraints on forward-declared classes?
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generics.m
#import <Foundation/Foundation.h>
@interface Base : NSObject
@end
@interface GenericCollection<T: Base *> : NSObject
@end
@class Derived2;
@interface Derived1 : Base
@property (strong) GenericCollection<Derived2 *> *collection;
@end
@interface Derived2 : Base
@property (strong) GenericCollection<Derived1 *> *collection;
@end
@mitzpettel
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mitzpettel commented May 1, 2016 •
edited
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Deferring the property declaration to a class extension works:

#import <Foundation/Foundation.h>

@interface Base : NSObject
@end

@interface GenericCollection<T: Base *> : NSObject
@end

@interface Derived1 : Base
@end

@interface Derived2 : Base
@property (strong) GenericCollection<Derived1 *> *collection;
@end

@interface Derived1 ()
@property (strong) GenericCollection<Derived2 *> *collection;
@end

In a real-world setting it would likely require introducing an additional header file that both Derived1.h and Derived2.h import.

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