RACDisposable
屬性方法
@interface RACDisposable : NSObject
1. @property (atomic, assign, getter = isDisposed, readonly) BOOL disposed;
2. + (instancetype)disposableWithBlock:(void (^)(void))block;
3. - (void)dispose;
4. - (RACScopedDisposable *)asScopedDisposable;
@end
