use sembar/lo in realworld

main.go

package main

import (
	"fmt"

	"github.com/samber/lo"
)

type User struct {
	ID int
}

func main() {
	users := []User{{1}, {2}, {3}}
	fmt.Println(old(users))
	fmt.Println(new(users))
}

func old(users []User) []int {
	ids := make([]int, 0, len(users))
	for _, v := range users {
		ids = append(ids, v.ID)
	}
	return ids
}

func new(users []User) []int {
	return lo.Map(users, func(u User, _ int) int { return u.ID })
}