Go struct memory packing

main.go

//  taken from https://play.golang.org/p/MBXg4UBOerp
package main

import (
	"fmt"
	"reflect"
)

type struct1 struct {
	field1 bool
	field2 bool
	field3 bool
	field4 int8
	field5 bool
}

type struct2 struct {
	field1 bool
	field2 bool
	field3 bool
	field4 int16
	field5 bool
}

type struct3 struct {
	field1 bool
	field2 bool
	field3 int16
	field4 int64
	field5 bool
}

// Random order
type struct4 struct {
	field1 bool
	field2 int64
	field3 bool
	field4 int64
	field5 bool
	field6 bool
	field7 bool
	field8 int64
	field9 bool
}

// Grouped by type
type struct5 struct {
	field1 bool
	field2 bool
	field3 bool
	field4 bool
	field5 bool
	field6 bool
	field7 int64
	field8 int64
	field9 int64
}

func detail(structType reflect.Type) {
	// Create a map of runes for each byte of the struct
	memoryMap := make([]rune, structType.Size())
	for i := range memoryMap {
		memoryMap[i] = '_'
	}

	fields := reflect.VisibleFields(structType)

	// Mark memory slots
	for _, field := range fields {
		for i := field.Offset; i < field.Offset+field.Type.Size(); i++ {
			// Set as last character of the field name
			memoryMap[i] = rune(field.Name[len(field.Name)-1])
		}
	}

	fmt.Printf("%d bytes:\t%s\n", structType.Size(), string(memoryMap))

}

func main() {
	fmt.Println("\nBiggest type size is 1 (bool, int8)")
	detail(reflect.TypeOf((struct1{})))

	fmt.Println("\nBiggest type size is 2 (int16)")
	detail(reflect.TypeOf((struct2{})))

	fmt.Println("\nBiggest type size is 8 (int64)")
	detail(reflect.TypeOf((struct3{})))

	fmt.Println("\nThese are same structs with different order:")
	detail(reflect.TypeOf((struct4{})))
	detail(reflect.TypeOf((struct5{})))
}