ReactiveObjC (二一)(RACEvent)

@interface RACEvent<__covariant ValueType> : NSObject 

+ (RACEvent *)completedEvent;
+ (RACEvent *)eventWithError:(nullable NSError *)error;
+ (RACEvent *)eventWithValue:(nullable ValueType)value;
@property (nonatomic, assign, readonly) RACEventType eventType;
@property (nonatomic, getter = isFinished, assign, readonly) BOOL finished;
@property (nonatomic, strong, readonly, nullable) NSError *error;
@property (nonatomic, strong, readonly, nullable) ValueType value;
@end