https://bswen.com/2021/03/others-golang-error1.html how to modify an element in slice when developing golang programs

.go

package main

import (
	"errors"
	"fmt"
)

type Book struct {
	ID     uint
	Title  string
	Author string
}

var Books []Book

func init() {
	Books = []Book {
		Book{
			ID: 1,
			Title: "aaaaaa",
			Author: "jack",
		},
		Book{
			ID: 2,
			Title: "bbbbbb",
			Author: "mike",
		},
	}
}


//not work
func ChangeABook1(bookId string,newTitle string)(bool,error) {
	defaultResult := false
	for _,book:=range Books {
		if idstring := fmt.Sprint(book.ID); idstring==bookId {
			book.Title = newTitle
			return true,nil
		}
	}
	return defaultResult,errors.New("not found "+bookId)
}

func ChangeABook2(bookId string,newTitle string)(bool,error) {
	defaultResult := false
	for idx,book:=range Books {
		if idstring := fmt.Sprint(book.ID); idstring==bookId {
			Books[idx].Title = newTitle
			return true,nil
		}
	}
	return defaultResult,errors.New("not found "+bookId)
}

func PrintBooks() {
	for _,book:=range Books {
		fmt.Printf("%v\n",book)
	}
}

func main_old() {
	book, err := FindABook("1")
	if err == nil {
		fmt.Printf(" got book %v\n", book)
	}else {
		fmt.Printf("%v\n",err)
	}
}

func main() {
	fmt.Print("before change\n")
	fmt.Print("===============\n")
	PrintBooks()
	ChangeABook2("1","newnewnewnnew")
	fmt.Print("\nafter change\n")
	fmt.Print("===============\n")
	PrintBooks()
}