附录-OC源码-Runtime：Clang 编译后的数据结构分析

typedef struct objc_object NSObject;  
typedef struct {} _objc_exc_NSObject;  
  
struct NSObject_IMPL {  
  Class isa;  
};  

typedef struct objc_object Test;  
typedef struct {} _objc_exc_Test;  
struct Test_IMPL {  
  struct NSObject_IMPL NSObject_IVARS;  
  NSNumber *testProperty1;  
  NSString *testProperty2;  
  Test *testProperty3;  
};  
  
static void _I_Test_testFunction(Test * self, SEL _cmd) {  
    printf("aaa");  
}  

// 类/成员变量定义: 没看懂  
extern "C" unsigned long int OBJC_IVAR_$_Test$testProperty1 __attribute__ ((used, section ("__DATA,__objc_ivar"))) = __OFFSETOFIVAR__(struct Test, testProperty1);  
  
//类或成员变量结构体:  _ivar_t  
struct _ivar_t {  
  unsigned long int *offset;  // pointer to ivar offset location  
  const char *name;  
  const char *type;  
  unsigned int alignment;  
  unsigned int  size;  
};  
  
// 类/成员变量结构体的 集合结构体: _ivar_list_t  
// 一个匿名结构体, 直接创建一个变量, _OBJC_$_INSTANCE_VARIABLES_Test  (后称Test_Var)  
static struct /*_ivar_list_t*/ {  
  unsigned int entsize;  // sizeof(struct _prop_t)  
  unsigned int count;  
  struct _ivar_t ivar_list[3];  
} _OBJC_$_INSTANCE_VARIABLES_Test __attribute__ ((used, section ("__DATA,__objc_const"))) = {  
  sizeof(_ivar_t),  
  3,  {
    {(unsigned long int *)&OBJC_IVAR_$_Test$testProperty1, "testProperty1", "@\"NSNumber\"", 3, 8},  
   {(unsigned long int *)&OBJC_IVAR_$_Test$testProperty2, "testProperty2", "@\"NSString\"", 3, 8},  
   {(unsigned long int *)&OBJC_IVAR_$_Test$testProperty3, "testProperty3", "@\"Test\"", 3, 8}}  
};  

// _objc_method  
struct _objc_method {  
  struct objc_selector * _cmd;  
  const char *method_type;  
  void  *_imp;  
};  
  
// 新建一个结构体 无名, 直接给变量  _OBJC_$_INSTANCE_METHODS_Test (后称Test_Method)  
// 方法列表: 单个大小, 方法数, 具体方法数组  
// 直接将 OC 语言中定义的函数名称赋值过来  
static struct /*_method_list_t*/ {  
  unsigned int entsize;  // sizeof(struct _objc_method)  
  unsigned int method_count;  
  struct _objc_method method_list[1];  
} _OBJC_$_INSTANCE_METHODS_Test __attribute__ ((used, section ("__DATA,__objc_const"))) = {  
  sizeof(_objc_method),  
  1,  
  {
    {(struct objc_selector *)"testFunction", "v16@0:8", (void *)_I_Test_testFunction}}  
};  

struct _class_ro_t {  
  unsigned int flags;  
  unsigned int instanceStart;  
  unsigned int instanceSize;  
  unsigned int reserved;  
  const unsigned char *ivarLayout;  
  const char *name;  
  const struct _method_list_t *baseMethods;  
  const struct _objc_protocol_list *baseProtocols;  
  const struct _ivar_list_t *ivars;  
  const unsigned char *weakIvarLayout;  
  const struct _prop_list_t *properties;  
};  
  
struct _class_t {  
  struct _class_t *isa;  
  struct _class_t *superclass;  
  void *cache;  
  void *vtable;  
  struct _class_ro_t *ro;  
};  

// 给 _class_ro_t 类型的结构体,建一个变量, 然后赋值,   
// 变量名: _OBJC_METACLASS_RO_$_Test  (后简称 MetaClass_OR_Test)  
// name: "Test"  
static struct _class_ro_t _OBJC_METACLASS_RO_$_Test __attribute__ ((used, section ("__DATA,__objc_const"))) = {  
  1, sizeof(struct _class_t), sizeof(struct _class_t),   
  (unsigned int)0,   
  0,   
  "Test",  
  (const struct _method_list_t *)&_OBJC_$_CLASS_METHODS_Test,  
  0,   
  0,   
  0,   
  0,   
};  
  
// 给 _class_ro_t 类型的结构体,建一个变量, 然后赋值,  
// 变量名: _OBJC_CLASS_RO_$_Test (后简称 Class_OR_Test)  
// name: "Test"  
// baseMethods: 将上面的 Test_Method 赋值过来  
// ivars: 将上面 Test_Var 赋值过来  
static struct _class_ro_t _OBJC_CLASS_RO_$_Test __attribute__ ((used, section ("__DATA,__objc_const"))) = {  
  0, __OFFSETOFIVAR__(struct Test, testProperty1), sizeof(struct Test_IMPL),   
  (unsigned int)0,   
  0,   
  "Test",  
  (const struct _method_list_t *)&_OBJC_$_INSTANCE_METHODS_Test,  
  0,   
  (const struct _ivar_list_t *)&_OBJC_$_INSTANCE_VARIABLES_Test,  
  0,   
  0,   
};  
  
// 给 _class_t 类型的结构体,建一个变量, 然后赋值,  
// 变量名: OBJC_METACLASS_$_Test (后简称 META_CLASS_Test)  
// ro 赋值为上面的  METACLASS_RO_Test  
extern "C" __declspec(dllexport) struct _class_t OBJC_METACLASS_$_Test __attribute__ ((used, section ("__DATA,__objc_data"))) = {  
  0, // &OBJC_METACLASS_$_NSObject,  
  0, // &OBJC_METACLASS_$_NSObject,  
  0, // (void *)&_objc_empty_cache,  
  0, // unused, was (void *)&_objc_empty_vtable,  
  &_OBJC_METACLASS_RO_$_Test,  
};  
  
extern "C" __declspec(dllimport) struct _class_t OBJC_CLASS_$_NSObject;  
// 给 _class_t 类型的结构体,建一个变量, 然后赋值,  
// 变量名: OBJC_CLASS_$_Test (后简称 CLASS_Test)  
// ro 赋值为上面的  CLASS_RO_Test  
extern "C" __declspec(dllexport) struct _class_t OBJC_CLASS_$_Test __attribute__ ((used, section ("__DATA,__objc_data"))) = {  
  0, // &OBJC_METACLASS_$_Test,  
  0, // &OBJC_CLASS_$_NSObject,  
  0, // (void *)&_objc_empty_cache,  
  0, // unused, was (void *)&_objc_empty_vtable,  
  &_OBJC_CLASS_RO_$_Test,  
};  
  
// 建立联系  
// META_Class_Test.isa 与 NSObject 的 meta 建立联系  
// META_Class_Test.superclass 也与 OBJC_METACLASS_$_NSObject 建立联系  
// METACLASS_$_Test.cache 给空  
// OBJC_CLASS_$_Test.isa 与 METACLASS 建立联系  
// OBJC_CLASS_$_Test.superclass 与OBJC_CLASS_$_NSObject; 建立联系  
// OBJC_CLASS_$_Test.cache 与 objc_empty_cache 建立联系  
static void OBJC_CLASS_SETUP_$_Test(void ) {  
  OBJC_METACLASS_$_Test.isa = &OBJC_METACLASS_$_NSObject;  
  OBJC_METACLASS_$_Test.superclass = &OBJC_METACLASS_$_NSObject;  
  OBJC_METACLASS_$_Test.cache = &_objc_empty_cache;  
  OBJC_CLASS_$_Test.isa = &OBJC_METACLASS_$_Test;  
  OBJC_CLASS_$_Test.superclass = &OBJC_CLASS_$_NSObject;  
  OBJC_CLASS_$_Test.cache = &_objc_empty_cache;  
}