From: Jeffrey Moss <jeff@...>
Date: 2005-03-24T08:41:48+09:00
Subject: Re: Credit Card Verification as an exercise

free your mind neo

right, there is no spoon

yeah

----- Original Message ----- 
From: "Florian Gross" <flgr@ccan.de>
Newsgroups: comp.lang.ruby
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Wednesday, March 23, 2005 4:34 PM
Subject: Re: Credit Card Verification as an exercise


> Jeffrey Moss wrote:
> 
>> Couldn't find any credit card verification code written in ruby so I
>> wrote up my own.  This code turns out a lot smaller than the perl
>> version I have been using.  I thought it was an interesting exercise,
>> here is how its done, if anybody can improve on what I've done I'd be
>> impressed. %*
> 
> Nice code and I guess it will be quite useful as well! Thanks for 
> posting this here.
> 
>> class CreditCard < ActiveRecord::Base
>> 
>>   def before_save
>>     if number_is_valid && number_matches_type
>>        ...
>>     end
>>   end
>> 
>>   def number_is_valid
> 
> Guess, I'd rename this to 'number_valid?'. :)
> 
>>     total = 0
>>     number.gsub(/[^0-9]/, '').reverse.scan(/(\d)(\d){0,1}/) do |ud,ad|
>>       (ad.to_i*2).to_s.each {|d| total = total + d.to_i} if ad
>>       total = total + ud.to_i
>>     end
>>     total % 10 == 0 ? false : true
> 
> Hm, why not simply "total % 10 != 0"?
> 
>>   end
>> 
>>   def number_matches_type
> 
> Might be nice to append a question mark here as well.
> 
>>     digit_length = number.length
>>     if card_type == 'visa'
>>       if (digit_length == 16) || (digit_length == 13)
>>         return true if number[/^\d/].to_i == 4
>>       end
>>     elsif card_type == 'mastercard'
>>       if digit_length == 16
>>         return true if (51..55).to_a.include?(number[0..1].to_i)
> 
> Hmmm, why the .to_a call?
> 
>>       end
>>     elsif card_type == 'amex'
>>       if digit_length == 15
>>         return true if [34,37].include?(number[0..1].to_i)
>>       end
>>     elsif card_type == 'discover'
>>       if digit_length == 16
>>         return true if number[0..3].to_i == 6011
>>       end
>>     end
>>   end
>> end
> 
> I think all this returns are superfluous -- after all Ruby will return 
> the result of evaluating the matching if clause.
> 
> Oh, and I think this is a good case for the case construct:
> 
> case card_type
>   when 'visa' then
>     [13, 16].include?(digit_length) and number[0, 1] == "4"
>   when 'mastercard' then
>     digit_length == 16 and ("51" .. "55").include?(number[0, 2])
>   when 'amex' then
>     digit_length == 15 and %w(34 37).include?(number[0, 2])
>   when 'discover' then
>     digit_length == 16 and number[0, 4] == "6011"
> end
>