background: on 64-bit operating system

example: define 2 stuct objects with the same members (in different order) and print

package main

import "unsafe"

type A struct {
    X bool
    Y float64
    Z int16
}

type B struct {
    Y float64
    X bool
    Z int16
}

func main() {
    print("A: ")
    println(unsafe.Sizeof(A{}))
    print("B: ")
    println(unsafe.Sizeof(B{}))
}

output result:

A: 24
B16

conclusion:
so when defining sturct members, random definitions may result in different memory usage. What I want to ask is, is there anything to refer to in the definition?