_Nullable: pointer may have a NULL or nil value while a _Nonnull one should not. The
compiler will tell you if you try to break the rules.
参考链接
Nullability and Objective-C
Objective-C 中 nullable、__nullable、_Nullable 的区别
_Nullable: pointer may have a NULL or nil value while a _Nonnull one should not. The
compiler will tell you if you try to break the rules.
Nullability and Objective-C
Objective-C 中 nullable、__nullable、_Nullable 的区别