Ruby flow control: throw an exception, return nil or let it fail?
control-flow, ruby, ruby-on-rails
Solution
1) Don't check anything and let the program fail (cleaner code, natural error messages):
It's ok to "let the program fail" with known, documented exceptions, but getting an unpleasant `NoMethodError` because you tried to use a `nil` object is just careless. In your particular example, `ActiveRecord#find` raises a documented `ActiveRecord::RecordNotFound` exception, so IMO this is the way to go:
def self.fetch(feed_id)
Feed.find(feed_id).fetch
end
2) Fail silently by returning nil (however, "Clean Code" says, that you should never return null):
That's fine as a general advice, but Ruby is crammed with methods that return `nil`; and that's ok (again, as long as it's documented), it just means "Nothing" (and allows the very compact pattern `something_that_can_be_nil || another_value`). In this case I'd write it concisely using Ick's `maybe`:
def self.fetch(feed_id)
Feed.find_by_id(feed_id).maybe.fetch
end
3) Throw exceptions (because it's exceptional not to find a feed by id):
Yes, but then let the method raise the well-known `RecordNotFound` exception, not a custom one (unless you want to abstract the fact that you are working with AR, which can be very cumbersome).
Problem
I am thinking of the best practices of flow control. Which way should I go? 1) Don't check anything and let the program fail (cleaner code, natural error messages): ``` def self.fetch(feed_id) feed = Feed.find(feed_id) feed.fetch end ``` 2) Fail silently by returning nil (however, "Clean Code" says, that you should never return null): ``` def self.fetch(feed_id) return unless feed_id feed = Feed.find(feed_id) return unless feed feed.fetch end ``` 3) Throw exceptions (because it's exceptional not to find a feed by id): ``` def self.fetch(feed_id) raise ArgumentError.new unless feed_id feed = Feed.find(feed_id) raise ArgumentError.new unless feed feed.fetch end ``` To put it in other words: should I be using guard conditions actively, or is it better to rely on Ruby / Rails methods and let them throw an exception, if something wrong happens?