Ruby Time Limitations

I ran across a strange problem recently dealing with the Ruby Time class. It seems that there is a limit imposed by various platforms as to the minimum value of a Ruby Time object. The problem reared it's head when I was creating a Ruby on Rails application that contained a user birthday. I mistakenly used Time for the birthday instead of Date.

The zero, minimum, and maximum times on my Mac are, respectively:

>> Time.at(0)
=> Wed Dec 31 17:00:00 MST 1969
>> Time.at(-2147483648)
=> Fri Dec 13 13:45:52 MST 1901
>> Time.at(2147483647)
=> Mon Jan 18 20:14:07 MST 2038

Not too bad, I can get back as far as 1901 and about 30 years into the future. However, when testing on my Windows XP machine I get:

>> Time.at(0)
=> Wed Dec 31 17:00:00 MST 1969
>> Time.at(-2147483648)
=> ArgumentError: time must be positive
        from (irb):4:in `at'
        from (irb):4
>> Time.at(2147483647)
=> Mon Jan 18 20:14:07 MST 2038

The big difference here, of course, is that 1969 is the beginning of time for a Ruby Time object on Windows. That's not very useful, so I switched from Time to Date for everything that did not need a time portion (duh!). The Ruby Date class has a much broader range of values and should be sufficient for any date needed. I would love to link to some other reference that verifies this so I know I'm not crazy, but I couldn't find anything that talked about this limitation.

Update: I found a Ruby on Rails ticket that talked about this problem, but it was closed as a Ruby problem, not a Rails problem. I searched the Ruby tickets and was unable to find anything. I opened ticket 11417 to track it, but it was rejected on the grounds that it is actually an msvcrt problem. Additionally, the time_t struct does not specify that negative values must be handled.

I guess the only workaround at this point is to use a DateTime instead of Time. However, this limitation on Windows does not allow you to use the ActiveSupport Time calculations like 50.years.ago. These operation will fail on Windows machines if they try to create a negative time.

---

• ← Previous Post
• Next Post →

---