@private

The instance variable is accessible only within the class that declares it.

@protected

The instance variable is accessible within the class that declares it and within classes that inherit it. All instance variables without an explicit scope directive have @protected scope.

@public

The instance variable is accessible everywhere.

@package

Using the modern runtime, an @package instance variable has @public scope inside the executable image that implements the class, but acts like @private outside.

The @package scope for Objective-C instance variables is analogous to private_extern for C variables and functions. Any code outside the class implementation’s image that tries to use the instance variable gets a link error.

This scope is most useful for instance variables in framework classes, where @private may be too restrictive but @protected or @public too permissive.