尝试分析Block结构

将以下代码变换为C++源代码，使用“clang -rewrite-objc main.m”操作。
说是C++，其实也仅仅是使用了struct结构，其本质上是C语言源代码。
main.m文件：

#import <Foundation/Foundation.h>
int main()
{
    void (^blk)(void)= ^{printf("Block\n");};
    blk();
    return 0;
}

转换后的main.cpp文件：

struct __block_impl {
    void *isa;
    int Flags;
    int Reserved;
    void *FuncPtr;
};


struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int flags=0) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};


static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
  printf("Block\n");
}


static struct __main_block_desc_0 {
  size_t reserved;
  size_t Block_size;
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0)};


int main()
{
    void (*blk)(void)= ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA));
    ((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);
    return 0;
}


static struct IMAGE_INFO { unsigned version; unsigned flag; } _OBJC_IMAGE_INFO = { 0, 2 };