像[self class]这样的宏

Question

我想创建返回自我类的宏。

MyCustomClass.m ：

static MyCustomClass *_instance = nil;  //not suitable
static [self class]  *_instance = nil;  //incorrect, but want like this
static SELF_CLASS    *_instance = nil;  //target 

如何创建这样的宏：

#define SELF_CLASS ...?...