OC泛型介绍

协议

@protocol Song <NSObject>

@end

Animal对象实现协议Song并定义泛型 ObjectType

#import <Foundation/Foundation.h>
#import "Song.h"

@interface Animal <__covariant ObjectType> : NSObject <Song>

@end

Dog对象继承Animal对象

#import <Foundation/Foundation.h>
#import "Animal.h"

@interface Dog <ObjectType> : Animal <ObjectType>

@end

Golden对象继承Dog对象并定义自己具体类型

#import "Dog.h"
#import "xxxObject.h"

NS_ASSUME_NONNULL_BEGIN

@interface Golden : Dog <xxxObject *>

@end

NS_ASSUME_NONNULL_END