Objective-C 之 Attribute & Package

中文難以表達原著的意思
Method and Class Attributes

Objective-C
now supports some gcc attributes for Objective-C methods.
Syntactically, attributes for a method follow the method's declaration,
and attributes for a method parameter sit between the parameter type and
the parameter name. Supported attributes include:

• Deprecation and availability, including AvailabilityMacros.h

  - (void)method:(id)param __attribute__((deprecated));

• Unused parameters

  - (void)method:(id) __attribute__((unused)) param;

• Sentinel parameters, including NS_REQUIRES_NIL_TERMINATION

  - (void)methodWithObjects:(id)obj, ... NS_REQUIRES_NIL_TERMINATION;

Objective-C
also supports some gcc attributes for Objective-C classes.
Syntactically, attributes for a class precede the class's @interface
declaration. Supported attributes include:

• Deprecation and availability, including AvailabilityMacros.h

  __attribute__((deprecated))

  @interface MyDeprecatedClass : SomeSuperclass

• Visibility

  __attribute__((visibility("hidden")))

  @interface MyPrivateClass : SomeSuperclass

@package Instance Variables

@package
is a new instance variable protection class, like @public
and @protected
. @package
instance variables behave as follows:

• @public
  in 32-bit;

• @public
  in 64-bit, inside the framework that defined the class;

• @private
  in 64-bit, outside the framework that defined the class.

In 64-bit, the instance variable symbol for an @package
ivar is not exported, so any attempt to use the ivar from outside the
framework that defined the class will fail with a link error. See "“64-bit Class and Instance Variable Access Control”

" for more about instance variable symbols.