Objective-C attribute & package

Difficult to express original meaning in Chinese
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, includingNS_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@package
Ivar is not exported, so any attempt to use the Ivar from outside
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.