How to check if a string is a valid date

Question

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

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.

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

Parsing dates can run into some gotcha's, especially when they are in a MM/DD/YYYY or DD/MM/YYYY format, such as short dates used in U.S. or Europe.

Date#parse attempts to figure out which to use, but there are many days in a month throughout the year when ambiguity between the formats can cause parsing problems.

I'd recommend finding out what the LOCALE of the user is, then, based on that, you'll know how to parse intelligently using Date.strptime. The best way to find where a user is located is to ask them during sign-up, and then provide a setting in their preferences to change it. Assuming you can dig it out by some clever heuristic and not bother the user for that information, is prone to failure so just ask.

This is a test using Date.parse. I'm in the U.S.:

>> Date.parse('01/31/2001')
ArgumentError: invalid date

>> Date.parse('31/01/2001') #=> #<Date: 2001-01-31 (4903881/2,0,2299161)>

The first was the correct format for the U.S.: mm/dd/yyyy, but Date didn't like it. The second was correct for Europe, but if your customers are predominately U.S.-based, you'll get a lot of badly parsed dates.

Ruby's Date.strptime is used like:

>> Date.strptime('12/31/2001', '%m/%d/%Y') #=> #<Date: 2001-12-31 (4904549/2,0,2299161)>

Date.valid_date? *date_string.split('-').reverse.map(&:to_i)

I'd like to extend Date class.

class Date
  def self.parsable?(string)
    begin
      parse(string)
      true
    rescue ArgumentError
      false
    end
  end
end

example

Date.parsable?("10-10-2010")
# => true
Date.parse("10-10-2010")
# => Sun, 10 Oct 2010
Date.parsable?("1")
# => false
Date.parse("1")
# ArgumentError: invalid date from (pry):106:in `parse'

Another way to validate date:

date_hash = Date._parse(date.to_s)
Date.valid_date?(date_hash[:year].to_i,
                 date_hash[:mon].to_i,
                 date_hash[:mday].to_i)