Go: Building Web Applications

Combining all three implementations

To close this chapter off with a bang, we will implement a mechanism in which each Avatar implementation takes a turn in trying to get the value. If the first implementation returns the ErrNoAvatarURL error, we will try the next and so on until we find a useable value.

In avatar.go, underneath the Avatar type, add the following type definition:

type TryAvatars []Avatar

The TryAvatars type is simply a slice of Avatar objects; therefore, we will add the following GetAvatarURL method:

func (a TryAvatars) GetAvatarURL(u ChatUser) (string, error) {
  for _, avatar := range a {
    if url, err := avatar.GetAvatarURL(u); err == nil {
      return url, nil
    }
  }
  return "", ErrNoAvatarURL
}

This means that TryAvatars is now a valid Avatar ...