合理组织struct结构以节省内存占用

struct 的排列不同，go 为其分配的内存空间也不同，下面的代码可以看到结果：

package main

import (
	"fmt"
	"unsafe"
)

type myStruct struct {
	myInt   bool    // 1 byte
	myFloat float64 // 8 bytes
	myBool  int32   // 4 bytes
}

type myStructOptimized struct {
	myFloat float64 // 8 bytes
	myInt   int32   // 4 bytes
	myBool  bool    // 1 byte
}

func main() {
	a := myStruct{}
	b := myStructOptimized{}

	fmt.Println(unsafe.Sizeof(a)) // unordered 24 bytes
	fmt.Println(unsafe.Sizeof(b)) // ordered 16 bytes
}

下面的代码可以验证struct 的内存分配：

package main

import (
	"fmt"
	"unsafe"
)

type myStructOptimized struct {
	myFloat float64 // 8 bytes
	myBool  bool    // 1 byte
	myInt   int32   // 4 bytes

}

func main() {
	b := myStructOptimized{}
	
	fmt.Println(unsafe.Sizeof(b))
	fmt.Println(unsafe.Offsetof(b.myFloat))
	fmt.Println(unsafe.Offsetof(b.myBool))
	fmt.Println(unsafe.Offsetof(b.myInt))
}

resource https://medium.com/@felipedutratine/how-to-organize-the-go-struct-in-order-to-save-memory-c78afcf59ec2 19