objective-c subscript

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

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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