What number distinctive annotations is accessible in Objective-C?

Here are the following distinctive annotations that are accessible in Objective C:

• _Null_unspecified, which bridges to a Swift certainly unwrapped optional. This is the default.
• _Nonnull, the esteem won’t be nil it bridges to a customary reference.
• _Nullable a value can be nil; it bridges to a discretionary.
• _Null_resettable this value can never be nil, when perused however you can set it to know to reset it. This just applies property.