Reducing nesting in Go functions with early returns

One of my favorite localized Go refactorings is reducing nesting by using return as early as possible. Take this example, based on a recently-refactored function at Heroku:

func example() error {
  if err := start(); err != nil {
    existing, err := fetchExisting()
    if err != nil {
      return err
    }

    if existing.IsWorking() {
      return nil
    } else {
      return errors.New("found existing but it's not working")
    }
  }

  return nil
}

This can be hard to follow due to nesting inside if ...; err != nil and use of else. I prefer to return as early as possible and avoid else. Applying that, it now looks something like this:

func example() error {
  if err := start(); err == nil {
    return err
  }

  existing, err := fetchExisting()
  if err != nil {
    return err
  }

  if !existing.IsWorking() {
    return errors.New("found existing but it's not working")
  }

  return nil
}

This style is mentioned in Effective Go but perhaps isn’t well-known enough. It’s a simple change but one that I feel greatly improves readability.

‹ Dan Peterson

Reducing nesting in Go functions with early returns

Nov 02, 2015