struct objc_class {
struct objc_class *isa;
};
struct objc_object {
struct objc_class *isa;
};
/// An opaque type that represents an Objective-C class.
typedef struct objc_class *Class; //类 (class object)
/// A pointer to an instance of a class.
typedef struct objc_object *id; //对象 (instance of class)
objc_class结构体内，有一个Class类型的变量叫isa，由上面可以知道Class是一个objc_class指针，因此isa是一个objc_class指针，通常如果在一个objc_object（下面会说到）中，也会有一个isa指针，指向的是这个对象所对应的类（objc_class）。 如果是在objc_class中的isa指针，指向的则是这个类的元类(metaClass）
创建类
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struct objc_object {
private:
isa_t isa;
public:
// ISA() assumes this is NOT a tagged pointer object
Class ISA();
// getIsa() allows this to be a tagged pointer object
Class getIsa();
// initIsa() should be used to init the isa of new objects only.
// If this object already has an isa, use changeIsa() for correctness.
// initInstanceIsa(): objects with no custom RR/AWZ
// initClassIsa(): class objects
// initProtocolIsa(): protocol objects
// initIsa(): other objects
void initIsa(Class cls /*nonpointer=false*/);
void initClassIsa(Class cls /*nonpointer=maybe*/);
void initProtocolIsa(Class cls /*nonpointer=maybe*/);
void initInstanceIsa(Class cls, bool hasCxxDtor);
// changeIsa() should be used to change the isa of existing objects.
// If this is a new object, use initIsa() for performance.
Class changeIsa(Class newCls);
bool hasNonpointerIsa();
bool isTaggedPointer();
bool isBasicTaggedPointer();
bool isExtTaggedPointer();
bool isClass();
// object may have associated objects?
bool hasAssociatedObjects();
void setHasAssociatedObjects();
// object may be weakly referenced?
bool isWeaklyReferenced();
void setWeaklyReferenced_nolock();
// object may have -.cxx_destruct implementation?
bool hasCxxDtor();
// Optimized calls to retain/release methods
id retain();
void release();
id autorelease();
// Implementations of retain/release methods
id rootRetain();
bool rootRelease();
id rootAutorelease();
bool rootTryRetain();
bool rootReleaseShouldDealloc();
uintptr_t rootRetainCount();
// Implementation of dealloc methods
bool rootIsDeallocating();
void clearDeallocating();
void rootDealloc();
private:
void initIsa(Class newCls, bool nonpointer, bool hasCxxDtor);
// Slow paths for inline control
id rootAutorelease2();
bool overrelease_error();
#if SUPPORT_NONPOINTER_ISA
// Unified retain count manipulation for nonpointer isa
id rootRetain(bool tryRetain, bool handleOverflow);
bool rootRelease(bool performDealloc, bool handleUnderflow);
id rootRetain_overflow(bool tryRetain);
bool rootRelease_underflow(bool performDealloc);
void clearDeallocating_slow();
// Side table retain count overflow for nonpointer isa
void sidetable_lock();
void sidetable_unlock();
void sidetable_moveExtraRC_nolock(size_t extra_rc, bool isDeallocating, bool weaklyReferenced);
bool sidetable_addExtraRC_nolock(size_t delta_rc);
size_t sidetable_subExtraRC_nolock(size_t delta_rc);
size_t sidetable_getExtraRC_nolock();
#endif
// Side-table-only retain count
bool sidetable_isDeallocating();
void sidetable_clearDeallocating();
bool sidetable_isWeaklyReferenced();
void sidetable_setWeaklyReferenced_nolock();
id sidetable_retain();
id sidetable_retain_slow(SideTable& table);
uintptr_t sidetable_release(bool performDealloc = true);
uintptr_t sidetable_release_slow(SideTable& table, bool performDealloc = true);
bool sidetable_tryRetain();
uintptr_t sidetable_retainCount();
#if DEBUG
bool sidetable_present();
#endif
};
objc_class
struct objc_class {
Class isa OBJC_ISA_AVAILABILITY;
#if !__OBJC2__
Class super_class OBJC2_UNAVAILABLE;
const char *name OBJC2_UNAVAILABLE;
long version OBJC2_UNAVAILABLE;
long info OBJC2_UNAVAILABLE;
long instance_size OBJC2_UNAVAILABLE;
struct objc_ivar_list *ivars OBJC2_UNAVAILABLE;
struct objc_method_list **methodLists OBJC2_UNAVAILABLE;
struct objc_cache *cache OBJC2_UNAVAILABLE;
struct objc_protocol_list *protocols OBJC2_UNAVAILABLE;
#endif
} OBJC2_UNAVAILABLE;
object_getClass源码：
Class object_getClass(id obj)
{
if (obj) return obj->getIsa();
else return Nil;
}
通过clang Dog.m
clang -rewrite-objc Dog.m
#import <Foundation/Foundation.h>
@interface Animal : NSObject
@end
@implementation Animal
@end
@interface Dog : Animal {
int age;
NSString *name;
}
- (void)instanceFun;
+ (void)classFun;
@end
@implementation Dog
- (void)instanceFun {
}
+ (void)classFun {
}
@end
extern "C" __declspec(dllexport) struct _class_t OBJC_METACLASS_$_Animal;
extern "C" __declspec(dllimport) struct _class_t OBJC_METACLASS_$_NSObject;
extern "C" __declspec(dllexport) struct _class_t OBJC_METACLASS_$_Dog __attribute__ ((used, section ("__DATA,__objc_data"))) = {
0, // &OBJC_METACLASS_$_NSObject,
0, // &OBJC_METACLASS_$_Animal,
0, // (void *)&_objc_empty_cache,
0, // unused, was (void *)&_objc_empty_vtable,
&_OBJC_METACLASS_RO_$_Dog,
};
extern "C" __declspec(dllexport) struct _class_t OBJC_CLASS_$_Animal;
extern "C" __declspec(dllexport) struct _class_t OBJC_CLASS_$_Dog __attribute__ ((used, section ("__DATA,__objc_data"))) = {
0, // &OBJC_METACLASS_$_Dog,
0, // &OBJC_CLASS_$_Animal,
0, // (void *)&_objc_empty_cache,
0, // unused, was (void *)&_objc_empty_vtable,
&_OBJC_CLASS_RO_$_Dog,
};
static void OBJC_CLASS_SETUP_$_Dog(void ) {
OBJC_METACLASS_$_Dog.isa = &OBJC_METACLASS_$_NSObject;
OBJC_METACLASS_$_Dog.superclass = &OBJC_METACLASS_$_Animal;
OBJC_METACLASS_$_Dog.cache = &_objc_empty_cache;
OBJC_CLASS_$_Dog.isa = &OBJC_METACLASS_$_Dog;
OBJC_CLASS_$_Dog.superclass = &OBJC_CLASS_$_Animal;
OBJC_CLASS_$_Dog.cache = &_objc_empty_cache;
}
static struct _class_ro_t _OBJC_METACLASS_RO_$_Dog __attribute__ ((used, section ("__DATA,__objc_const"))) = {
1, sizeof(struct _class_t), sizeof(struct _class_t),
(unsigned int)0,
0,
"Dog",
(const struct _method_list_t *)&_OBJC_$_CLASS_METHODS_Dog,
0,
0,
0,
0,
};
static struct _class_ro_t _OBJC_CLASS_RO_$_Dog __attribute__ ((used, section ("__DATA,__objc_const"))) = {
0, __OFFSETOFIVAR__(struct Dog, age), sizeof(struct Dog_IMPL),
(unsigned int)0,
0,
"Dog",
(const struct _method_list_t *)&_OBJC_$_INSTANCE_METHODS_Dog,
0,
(const struct _ivar_list_t *)&_OBJC_$_INSTANCE_VARIABLES_Dog,
0,
0,
};
extern "C" __declspec(dllexport) struct _class_t OBJC_METACLASS_$_Animal;
extern "C" __declspec(dllimport) struct _class_t OBJC_METACLASS_$_NSObject;
extern "C" __declspec(dllexport) struct _class_t OBJC_METACLASS_$_Dog __attribute__ ((used, section ("__DATA,__objc_data"))) = {
0, // &OBJC_METACLASS_$_NSObject,
0, // &OBJC_METACLASS_$_Animal,
0, // (void *)&_objc_empty_cache,
0, // unused, was (void *)&_objc_empty_vtable,
&_OBJC_METACLASS_RO_$_Dog,
};
实例方法和实例变量应该被加到类中。类方法被加到元类中。
static struct /*_method_list_t*/ {
unsigned int entsize; // sizeof(struct _objc_method)
unsigned int method_count;
struct _objc_method method_list[1];
} _OBJC_$_INSTANCE_METHODS_Dog __attribute__ ((used, section ("__DATA,__objc_const"))) = {
sizeof(_objc_method),
1,
{{(struct objc_selector *)"instanceFun", "v16@0:8", (void *)_I_Dog_instanceFun}}
};
static struct /*_method_list_t*/ {
unsigned int entsize; // sizeof(struct _objc_method)
unsigned int method_count;
struct _objc_method method_list[1];
} _OBJC_$_CLASS_METHODS_Dog __attribute__ ((used, section ("__DATA,__objc_const"))) = {
sizeof(_objc_method),
1,
{{(struct objc_selector *)"classFun", "v16@0:8", (void *)_C_Dog_classFun}}
};
+ (Class)class {
return self;
}
- (Class)class {
return object_getClass(self);
}
BOOL class_isMetaClass(Class cls)
{
if (!cls) return NO;
return cls->isMetaClass();
}
bool isMetaClass() {
return info & CLS_META;
}
