Package errgroup has a Go method that takes a function and calls it inside a new goroutine. It’s so convenient when you use goroutines and want to handle their errors in one place. Maybe I’ll write such code more often than plain goroutines.
package mainimport ( "encoding/json" "fmt" "log" "net/http" "golang.org/x/sync/errgroup")func main() { userID := 1 user, err := fetchUserByID(userID) if err != nil { log.Fatalf("failed to fetch user: %v", err) } var posts []Post var todos []Todo errGroup := new(errgroup.Group) errGroup.Go(func() error { var err error posts, err = fetchPostsByUserID(user.ID) return err }) errGroup.Go(func() error { var err error todos, err = fetchTodosByUserID(user.ID) return err }) if err := errGroup.Wait(); err != nil { log.Fatalf("error fetching posts or todos: %v", err) } fmt.Println("time taken:", elapsed) fmt.Printf("user: %+v\n", user) fmt.Printf("posts: %+v\n", posts) fmt.Printf("todos: %+v\n", todos)}// Structs for JSONPlaceholder API responsestype User struct { ID int `json:"id"` Name string `json:"name"`}type Post struct { ID int `json:"id"` UserID int `json:"userId"` Title string `json:"title"` Body string `json:"body"`}type Todo struct { ID int `json:"id"` UserID int `json:"userId"` Title string `json:"title"` IsCompleted bool `json:"completed"`}// Fetch functions for JSONPlaceholder APIconst baseURL = "https://jsonplaceholder.typicode.com"func fetchUserByID(id int) (User, error) { url := fmt.Sprintf("%s/users/%d", baseURL, id) return fetchByURL[User](url)}func fetchTodosByUserID(userID int) ([]Todo, error) { url := fmt.Sprintf("%s/users/%d/todos", baseURL, userID) return fetchByURL[[]Todo](url)}func fetchPostsByUserID(userID int) ([]Post, error) { url := fmt.Sprintf("%s/users/%d/posts", baseURL, userID) return fetchByURL[[]Post](url)}func fetchByURL[T any](url string) (T, error) { res, err := http.Get(url) if err != nil { var zero T return zero, err } defer res.Body.Close() if res.StatusCode != http.StatusOK { var zero T return zero, fmt.Errorf("failed to fetch data from %s: status code %d", url, res.StatusCode) } var value T if err := json.NewDecoder(res.Body).Decode(&value); err != nil { var zero T return zero, err } return value, nil}
