post: add go empty struct

content/posts/2023/09/_index.md

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+---
+weight: 1
+bookCollapseSection: true
+title: "09"
+---

content/posts/2023/09/go_empty_struct.md

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+---
+author: "jdlau"
+date: 2023-09-01
+linktitle: Go Empty Struct
+menu:
+next:
+prev:
+title: Go Empty Struct
+weight: 10
+categories: ['Go']
+tags: ['mark']
+---
+
+```go
+package main
+
+import (
+	"fmt"
+	"unsafe"
+)
+
+func main() {
+	type A struct{}
+	type B struct{}
+    // 结构体里的字段都是`Empty Struct`时，占用空间为0
+	type S struct {
+		A A
+		B B
+	}
+	var s S
+	fmt.Println(unsafe.Sizeof(s)) // prints 0
+    // 如果是指针，占用空间为8
+	fmt.Println(unsafe.Sizeof(&s)) // prints 8
+
+	var x [1000000000]struct{}
+    // 可以同时存储A和B类型元素
+	x[0] = A{}
+	x[1] = B{}
+	fmt.Println(unsafe.Sizeof(x)) // prints 0
+    // 地址一样
+	fmt.Printf("%p, %p", &x[0], &x[1]) // 0x54e3a0, 0x54e3a0
+}
+```
+
+[See also](https://dave.cheney.net/2014/03/25/the-empty-struct)