Misleading DateTime comparison

rubyonrails-talk
1

I think the most natural way read the code created_at < 10.minutes.ago is “created_at is less than ten minutes ago,” but that reading suggests the mistaken interpretation that created_at is fewer than ten minutes ago. The correct interpretation is that created_at is earlier than ten minutes ago. Is there a better way to write the same comparison?

I’ve thought of three potential improvements so far:

  • 10.minutes.ago > created_at This “Yoda condition” style doesn’t have a translation into ordinary English that tempts you into misunderstanding. But Yoda conditions are inconsistent with the rest of the comparisons in my codebase.
  • Time.now > 10.minutes.after(created_at) This is another style of Yoda condition. This one allows people who misread the operator (as “more than ten minutes after created_at” instead of “later than ten minutes after created_at”) to correctly predict the actual behavior, but for the wrong reason.
  • created_at.earlier_than?(10.minutes.ago) The ordinary English translation (created_at is earlier than ten minutes ago) is correct. But this requires monkeypatching DateTime (or using the human_time gem) to add the earlier_than? method, which I’d prefer not to do. Is there a better way that avoids Yoda conditionals, monkeypatching and extra gems?

Thanks for the consideration,

Nate

2

It never occurred to me that there is any confusion over this syntax. created_at is a time, 10 minutes ago is a time, time a < time b is unambiguous.

Colin

3

I think the real issue is that English lacks strong typing and so the comparison operater is imprecise.