Attributes in Clang

Clang官方文档：Clang documentation

• objc_runtime_name
  用于 @interface 或 @protocol，指定类或协议编译后的名字
  attribute((objc_runtime_name("MyLocalName")))
  @interface Message
  @end
  // (lldb) po [self class]
  // MyLocalName

• objc_requires_super
  指定子类覆写该方法时需要调用父类方法

The attribute to designate that a method requires a “call to super
” in the overriding method in the subclass.

  - (void)foo __attribute__((objc_requires_super));

• objc_subclassing_restricted
  禁止继承
  attribute((objc_subclassing_restricted))
  @interface A : NSObject
  @end

  @interface B : A //  Cannot subclass a class with objc_subclassing_restricted attribute
  @end
  

• objc_runtime_visible
  禁止继承和category

This attribute specifies that the Objective-C class to which it applies is visible to the Objective-C runtime but not to the linker. Classes annotated with this attribute cannot be subclassed and cannot have categories defined for them.

• constructor / destructor
  添加这两个属性的函数会在分别在可执行文件（或 shared library）load 和 unload 时被调用，即main()函数调用前和main()函数return后执行，执行顺序：+load -> constructor -> main -> destructor

  __attribute__((constructor))
  static void beforeMain(void) {
      NSLog(@"%s", __func__);  // beforeMain 
  }
  
  __attribute__((destructor))
  static void afterMain(void) {
      NSLog(@"%s", __func__);  // afterMain (main函数return后执行)
  }
  

  constructor可控制优先级，如__attribute__((constructor(101)))，数字越小优先级越高，1-100为系统保留。

• cleanup
  声明的变量作用域结束后调用指定函数

  {
      __strong XXObject *obj __attribute__((cleanup(cleanuptest))) = [[XXObject alloc]init];
      [obj test];
  }
  NSLog(@"end");
  

  static void cleanuptest(__strong XXObject **obj)
  {
      XXObject *obj_t = *obj;
      NSLog(@"%s", __func__);
  }
  
  // 2016-05-25 15:38:08.350 Test[2559:159531] cleanuptest
  // 2016-05-25 15:38:08.350 Test[2559:159531] -[XXObject dealloc]
  // 2016-05-25 15:38:08.350 Test[2559:159531] end