Go's errors.Join

Sat, 27 Jun 2026 00:00:00 +0000

Before Go 1.20, returning “here is everything that’s wrong” meant building your own error slice type. Now the standard library does it:

func validate(u User) error {
    var errs error
    if u.Name == "" {
        errs = errors.Join(errs, errors.New("name is required"))
    }
    if u.Age < 0 {
        errs = errors.Join(errs, errors.New("age must be non-negative"))
    }
    return errs // nil if nothing was joined
}

errors.Join ignores nil arguments, so the accumulate-in-a-loop pattern just works. And errors.Is / errors.As still see through the joined result to each underlying error.

errors on semikolan

Go's errors.Join