参考：https://www.jianshu.com/p/75110e335f37
参考：https://www.jianshu.com/p/68598c0f5aee
现实中
在oc语言世界里，下标语法使用很常见。
例如：
NSDictionary* dict = [[NSDictionary alloc] init];
dict[@"key1"] = @"value1";
NSArray* arr = [[NSArray alloc] init];
arr[0] = @"value1";
问题
那么问题来了，如果让你自定义一个类，实现下标操作呢？
官方的文档已经提供了相应的说明
image.png
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NSDictionary
- (nullable ObjectType)objectForKeyedSubscript:(KeyType)key
- (void)setObject:(nullable ObjectType)obj forKeyedSubscript:(KeyType <NSCopying>)key;
NSArray
- (ObjectType)objectAtIndex:(NSUInteger)index;
- (void)setObject:(ObjectType)obj atIndexedSubscript:(NSUInteger)idx;
自定义类
@interface TestDictionary : NSObject
- (nullable ObjectType)objectForKeyedSubscript:(KeyType)key
- (void)setObject:(RACSignal *)signal forKeyedSubscript:(NSString *)keyPath;
@end
RAC框架
@interface RACSubscriptingAssignmentTrampoline : NSObject
- (nullable instancetype)initWithTarget:(nullable id)target nilValue:(nullable id)nilValue;
- (void)setObject:(RACSignal *)signal forKeyedSubscript:(NSString *)keyPath;
@end
