核心是类模型
1 isEqual
内部实现比较指针是否相等
if (self == other) return YES;
if (!self || !other) return NO;
2 performSelector
((id(*)(id, SEL))objc_msgSend)((id)self, sel);
3 isMemberOfClass

• (BOOL)isMemberOfClass:(Class)cls {
  return [self class] == cls;
  }
  4

• (BOOL)isKindOfClass:(Class)cls {
  for (Class tcls = object_getClass((id)self); tcls; tcls = tcls->superclass) {
  if (tcls == cls) return YES;
  }
  return NO;
  }
  5
• (BOOL)isSubclassOfClass:(Class)cls {
  for (Class tcls = self; tcls; tcls = tcls->superclass) {
  if (tcls == cls) return YES;
  }
  return NO;
  }
  6
• (BOOL)conformsToProtocol:(Protocol *)protocol {
  if (!protocol) return NO;
  for (Class tcls = self; tcls; tcls = tcls->superclass) {
  if (class_conformsToProtocol(tcls, protocol)) return YES;
  }
  return NO;
  }
  7 这里验证了类模型的争取性
• (BOOL)respondsToSelector:(SEL)sel {
  if (!sel) return NO;
  return class_respondsToSelector_inst(object_getClass(self), sel, self);
  }

• (BOOL)respondsToSelector:(SEL)sel {
  if (!sel) return NO;
  return class_respondsToSelector_inst([self class], sel, self);
  }