How to check if a string is a valid date

d, m, y = date_string.split '-'
Date.valid_date? y.to_i, m.to_i, d.to_i

Here is a simple one liner:

DateTime.parse date rescue nil

I probably wouldn't recommend doing exactly this in every situation in real life as you force the caller to check for nil, eg. particularly when formatting. If you return a default date|error it may be friendlier.

require 'date'
begin
   Date.parse("31-02-2010")
rescue ArgumentError
   # handle invalid date
end