objc-class-relations-main-code

gistfile1.txt

//object.mm && objc.h
typedef struct objc_class *Class;
typedef struct objc_object *id;

//NSObject.mm
@interface NSObject <NSObject> {
    Class isa  OBJC_ISA_AVAILABILITY;
}

+ (Class)class {
    return self;
}

- (Class)class {
    return object_getClass(self);
}

//objc-class.mm
Class object_getClass(id obj)
{
    if (obj) return obj->getIsa();
    else return Nil;
}

//objc-private.h
struct objc_object {
private:
    isa_t isa;
    ...
}

union isa_t
{
    isa_t() { }
    isa_t(uintptr_t value) : bits(value) { }

    Class cls;
    uintptr_t bits;
}

inline Class
objc_object::ISA()
{
    assert(!isTaggedPointer());
    return isa.cls;
}

//objc-object.h
inline Class
objc_object::getIsa()
{
#if SUPPORT_TAGGED_POINTERS
    if (isTaggedPointer()) {
        uintptr_t slot = ((uintptr_t)this >> TAG_SLOT_SHIFT) & TAG_SLOT_MASK;
        return objc_tag_classes[slot];
    }
#endif
    return ISA();
}

//objc-runtime-old.h
struct objc_class : objc_object {
    Class superclass;
    const char *name;
    uint32_t version;
    uint32_t info;
    uint32_t instance_size;
    struct old_ivar_list *ivars;
    struct old_method_list **methodLists;
    Cache cache;
    struct old_protocol_list *protocols;
    // CLS_EXT only
    const uint8_t *ivar_layout;
    struct old_class_ext *ext;
    ...
}