@interface NSObject <NSObject> {
    Class isa  OBJC_ISA_AVAILABILITY;
}

+ (void)load;

+ (void)initialize;
- (instancetype)init
#if NS_ENFORCE_NSOBJECT_DESIGNATED_INITIALIZER
    NS_DESIGNATED_INITIALIZER
#endif
    ;

+ (instancetype)new OBJC_SWIFT_UNAVAILABLE("use object initializers instead");
+ (instancetype)allocWithZone:(struct _NSZone *)zone OBJC_SWIFT_UNAVAILABLE("use object initializers instead");
+ (instancetype)alloc OBJC_SWIFT_UNAVAILABLE("use object initializers instead");
- (void)dealloc OBJC_SWIFT_UNAVAILABLE("use 'deinit' to define a de-initializer");

- (void)finalize;

....

- (id)copy;
- (id)mutableCopy;

+ (id)copyWithZone:(struct _NSZone *)zone OBJC_ARC_UNAVAILABLE;
+ (id)mutableCopyWithZone:(struct _NSZone *)zone OBJC_ARC_UNAVAILABLE;

+ (BOOL)instancesRespondToSelector:(SEL)aSelector;
+ (BOOL)conformsToProtocol:(Protocol *)protocol;
- (IMP)methodForSelector:(SEL)aSelector;
+ (IMP)instanceMethodForSelector:(SEL)aSelector;
- (void)doesNotRecognizeSelector:(SEL)aSelector;

+ (NSMethodSignature *)instanceMethodSignatureForSelector:(SEL)aSelector OBJC_SWIFT_UNAVAILABLE("");

- (BOOL)allowsWeakReference UNAVAILABLE_ATTRIBUTE;
- (BOOL)retainWeakReference UNAVAILABLE_ATTRIBUTE;

+ (BOOL)isSubclassOfClass:(Class)aClass;

+ (BOOL)resolveClassMethod:(SEL)sel OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);
+ (BOOL)resolveInstanceMethod:(SEL)sel OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);

+ (Class)superclass;
+ (Class)class OBJC_SWIFT_UNAVAILABLE("use 'aClass.self' instead");

- (id)forwardingTargetForSelector:(SEL)aSelector OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);
- (void)forwardInvocation:(NSInvocation *)anInvocation OBJC_SWIFT_UNAVAILABLE("");
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector OBJC_SWIFT_UNAVAILABLE("");

+ (NSUInteger)hash;
+ (NSString *)description;
+ (NSString *)debugDescription;

@implementation SwiftObject
+ (void)initialize {}

+ (instancetype)allocWithZone:(struct _NSZone *)zone {
  assert(zone == nullptr);
  return _allocHelper(self);
}

+ (instancetype)alloc {
  // we do not support "placement new" or zones,
  // so there is no need to call allocWithZone
  return _allocHelper(self);
}

+ (Class)class {
  return self;
}
- (Class)class {
  return (Class) _swift_getClassOfAllocated(self);
}
+ (Class)superclass {
  return (Class) _swift_getSuperclass((const ClassMetadata*) self);
}
- (Class)superclass {
  return (Class) _swift_getSuperclass(_swift_getClassOfAllocated(self));
}

+ (BOOL)isMemberOfClass:(Class)cls {
  return cls == (Class) _swift_getClassOfAllocated(self);
}

- (BOOL)isMemberOfClass:(Class)cls {
  return cls == (Class) _swift_getClassOfAllocated(self);
}

- (instancetype)self {
  return self;
}
- (BOOL)isProxy {
  return NO;
}

- (struct _NSZone *)zone {
  auto zone = malloc_zone_from_ptr(self);
  return (struct _NSZone *)(zone ? zone : malloc_default_zone());
}

- (void)doesNotRecognizeSelector: (SEL) sel {
  Class cls = (Class) _swift_getClassOfAllocated(self);
  fatalError(/* flags = */ 0,
             "Unrecognized selector %c[%s %s]\n",
             class_isMetaClass(cls) ? '+' : '-', 
             class_getName(cls), sel_getName(sel));
}

- (id)retain {
  auto SELF = reinterpret_cast<HeapObject *>(self);
  swift_retain(SELF);
  return self;
}
- (void)release {
  auto SELF = reinterpret_cast<HeapObject *>(self);
  swift_release(SELF);
}
- (id)autorelease {
  return _objc_rootAutorelease(self);
}
- (NSUInteger)retainCount {
  return swift::swift_retainCount(reinterpret_cast<HeapObject *>(self));
}
- (BOOL)_isDeallocating {
  return swift_isDeallocating(reinterpret_cast<HeapObject *>(self));
}
- (BOOL)_tryRetain {
  return swift_tryRetain(reinterpret_cast<HeapObject*>(self)) != nullptr;
}
- (BOOL)allowsWeakReference {
  return !swift_isDeallocating(reinterpret_cast<HeapObject *>(self));
}
- (BOOL)retainWeakReference {
  return swift_tryRetain(reinterpret_cast<HeapObject*>(self)) != nullptr;
}

// Retaining the class object itself is a no-op.
+ (id)retain {
  return self;
}
+ (void)release {
  /* empty */
}
+ (id)autorelease {
  return self;
}
+ (NSUInteger)retainCount {
  return ULONG_MAX;
}
+ (BOOL)_isDeallocating {
  return NO;
}
+ (BOOL)_tryRetain {
  return YES;
}
+ (BOOL)allowsWeakReference {
  return YES;
}
+ (BOOL)retainWeakReference {
  return YES;
}

- (void)dealloc {
  swift_rootObjCDealloc(reinterpret_cast<HeapObject *>(self));
}

- (BOOL)isKindOfClass:(Class)someClass {
  for (auto isa = _swift_getClassOfAllocated(self); isa != nullptr;
       isa = _swift_getSuperclass(isa))
    if (isa == (const ClassMetadata*) someClass)
      return YES;

  return NO;
}

+ (BOOL)isSubclassOfClass:(Class)someClass {
  for (auto isa = (const ClassMetadata*) self; isa != nullptr;
       isa = _swift_getSuperclass(isa))
    if (isa == (const ClassMetadata*) someClass)
      return YES;

  return NO;
}

+ (BOOL)respondsToSelector:(SEL)sel {
  if (!sel) return NO;
  return class_respondsToSelector((Class) _swift_getClassOfAllocated(self), sel);
}

- (BOOL)respondsToSelector:(SEL)sel {
  if (!sel) return NO;
  return class_respondsToSelector((Class) _swift_getClassOfAllocated(self), sel);
}

+ (BOOL)instancesRespondToSelector:(SEL)sel {
  if (!sel) return NO;
  return class_respondsToSelector(self, sel);
}

- (BOOL)conformsToProtocol:(Protocol*)proto {
  if (!proto) return NO;
  auto selfClass = (Class) _swift_getClassOfAllocated(self);
  
  // Walk the superclass chain.
  while (selfClass) {
    if (class_conformsToProtocol(selfClass, proto))
      return YES;
    selfClass = class_getSuperclass(selfClass);
  }

  return NO;
}

+ (BOOL)conformsToProtocol:(Protocol*)proto {
  if (!proto) return NO;

  // Walk the superclass chain.
  Class selfClass = self;
  while (selfClass) {
    if (class_conformsToProtocol(selfClass, proto))
      return YES;
    selfClass = class_getSuperclass(selfClass);
  }
  
  return NO;
}

- (NSUInteger)hash {
  return (NSUInteger)self;
}

- (BOOL)isEqual:(id)object {
  return self == object;
}

- (id)performSelector:(SEL)aSelector {
  return ((id(*)(id, SEL))objc_msgSend)(self, aSelector);
}

- (id)performSelector:(SEL)aSelector withObject:(id)object {
  return ((id(*)(id, SEL, id))objc_msgSend)(self, aSelector, object);
}

- (id)performSelector:(SEL)aSelector withObject:(id)object1
                                     withObject:(id)object2 {
  return ((id(*)(id, SEL, id, id))objc_msgSend)(self, aSelector, object1,
                                                                 object2);
}

- (NSString *)description {
  return _getDescription(self);
}
- (NSString *)debugDescription {
  return _getDescription(self);
}

+ (NSString *)description {
  return _getClassDescription(self);
}
+ (NSString *)debugDescription {
  return _getClassDescription(self);
}

- (NSString *)_copyDescription {
  // The NSObject version of this pushes an autoreleasepool in case -description
  // autoreleases, but we're OK with leaking things if we're at the top level
  // of the main thread with no autorelease pool.
  return [[self description] retain];
}

- (CFTypeID)_cfTypeID {
  // Adopt the same CFTypeID as NSObject.
  static CFTypeID result;
  static dispatch_once_t predicate;
  dispatch_once_f(&predicate, &result, [](void *resultAddr) {
    id obj = [[NSObject alloc] init];
    *(CFTypeID*)resultAddr = [obj _cfTypeID];
    [obj release];
  });
  return result;
}

// Foundation collections expect these to be implemented.
- (BOOL)isNSArray__      { return NO; }
- (BOOL)isNSDictionary__ { return NO; }
- (BOOL)isNSSet__        { return NO; }
- (BOOL)isNSOrderedSet__ { return NO; }
- (BOOL)isNSNumber__     { return NO; }
- (BOOL)isNSData__       { return NO; }
- (BOOL)isNSDate__       { return NO; }
- (BOOL)isNSString__     { return NO; }
- (BOOL)isNSValue__      { return NO; }

@end

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;