6. 大小为 0 字节的变量

• 空结构体的大小是 0，所有空结构体的值都指向同一个指针 zerobase

  // base address for all 0-byte allocations
  var zerobase uintptr
  

示例代码：

type A struct {
}

type B struct {
	a A
	b int
}

func main() {
	a := A{}
	b := B{}
	c := A{}
	fmt.Printf("a pointer is: %p, size is %dbytes\n", &a, unsafe.Sizeof(a))
	fmt.Printf("b pointer is: %p, size is %dbytes\n", &b, unsafe.Sizeof(b))
  fmt.Printf("b.a pointer is: %p, size is %dbytes\n", &b.a, unsafe.Sizeof(b.a))  //b中的a非独立，需要依赖于b
	fmt.Printf("c pointer is: %p, size is %dbytes\n", &c, unsafe.Sizeof(c))
}

//输出
/*
a pointer is: 0x1164fc0, size is 0bytes
b pointer is: 0xc000096008, size is 8bytes
b.a pointer is: 0xc00010c008, size is 0bytes
c pointer is: 0x1164fc0, size is 0bytes
*/

作用：节约内存

• 传递信号，如 channel
• HashSet 的 Value