# Object Troubles - undefined method \`+' **URL:** \ **Category:** Ruby\ **Created:** [June 5, 2006, 10:01pm UTC](https://www.ruby-forum.com/t/object-troubles-undefined-method/62528 "2006-06-05T22:01:32Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Paul\_DSKraus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ed655f/32.png) [@Paul\_DSKraus](https://www.ruby-forum.com/u/Paul_DSKraus)\ **Post date:** [June 5, 2006, 10:01pm UTC](https://www.ruby-forum.com/t/object-troubles-undefined-method/62528/1 "2006-06-05T22:01:32Z")
I am parsing a text file that is 3 fields per line deliminted by pipes ‘|’ Each line contains a customer code, shipmethod, and customer name. Each line represents an invoice that was cut. I need to count all invoices and then count all invoices that went out next day air saver. From working with the pick axe it seems to me that you have a class with two attributes invoice, and nda invoice. You then store your objects in a hash for easy lookup. When i run the below program I get this error… ./parse.rb:14:in `incndainvoice': undefined method`+’ for nil:NilClass (NoMethodError) from ./parse.rb:31 from ./parse.rb:20 TIA, Paul Here is my class and program … #!/usr/bin/env ruby class Customer attr\_reader :invoices, :ndainvoices attr\_writer :invoices, :ndainvoices def initialize @invoices = 1 @ndainvoices = 0 end def increment\_invoice invoices = invoices + 1 end def increment\_ndainvoice ndainvoice = ndainvoice + 1 end end customers = Hash.new # open(‘NdaInvoiceCount.txt’,‘r’).each\_line do |line| (customer\_code, ship\_method, customer\_name) = line.chomp.split(’|’) if customers[customer\_code] customers[customer\_code].increment\_invoice else customers[customer\_code] = Customer.new end customers[customer\_code].increment\_ndainvoice if ship\_method ‘SAVGRD’ end here is some sample data… 0000016324|SAVGRD|Dupage Prosthetics 0000038955|SAVGRD|TRUDELL ORTH & PROS SERVICES 0000019155|UPS |Scott Orthotic Labs 0000061674|UPS |COMPREHENSIVE BRACE & LIMB CTR LLC 0000008593|U02G |Huron Valley Assoc 0000039954|SAVGRD|Island Coast Orthopedics 0000028719|UPS |Paul Richelson’s Feet First 0000003455|FEDGND|CLARK ORTH 0000019297|UPS |J. Slawner LTD. 0000061508|UPS |LEVY & RAPPEL ---
**Author:** ![Paul\_DSKraus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ed655f/32.png) [@Paul\_DSKraus](https://www.ruby-forum.com/u/Paul_DSKraus)\ **Post date:** [June 5, 2006, 10:13pm UTC](https://www.ruby-forum.com/t/object-troubles-undefined-method/62528/2 "2006-06-05T22:13:57Z")
> class Customer > attr\_reader :invoices, :ndainvoices > attr\_writer :invoices, :ndainvoices > def initialize > @invoices = 1 > @ndainvoices = 0 Here you initialize 2 _instance_ variables, @invoices and @ndainvoices end > def increment\_invoice > invoices = invoices + 1 The _local_ variable ‘invoices’ does exist yet, so ‘nil + 1’ raises the error. You probably intended: @invoices = @invoices + 1 end > def increment\_ndainvoice > ndainvoice = ndainvoice + 1 same here end ---
**Author:** ![Paul\_DSKraus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ed655f/32.png) [@Paul\_DSKraus](https://www.ruby-forum.com/u/Paul_DSKraus)\ **Post date:** [June 5, 2006, 10:18pm UTC](https://www.ruby-forum.com/t/object-troubles-undefined-method/62528/3 "2006-06-05T22:18:09Z")
On Jun 5, 2006, at 10:00 PM, Paul D. Kraus wrote: > def increment\_ndainvoice > ndainvoice = ndainvoice + 1 > end You are trying to set local variables. Instance variables are prefixed with @. If you were trying to call your attr\_writer method, you need to prefix it with self: self.invoices += 1 Here is a more idiomatic way of writing what you would like: class Customer attr\_accessor :invoices, :ndainvoices def initialize @invoices = 0 @ndainvoices = 0 end end customers = Hash.new { |h, k| h[k] = Customer.new } IO.foreach(‘NdaInvoiceCount.txt’) do |line| (customer\_code, ship\_method, customer\_name) = line.chomp.split(’|’) customers[customer\_code].invoices += 1 customers[customer\_code].ndainvoices += 1 if ship\_method == ‘SAVGRD’ end – Daniel ---
**Author:** ![Paul\_DSKraus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ed655f/32.png) [@Paul\_DSKraus](https://www.ruby-forum.com/u/Paul_DSKraus)\ **Post date:** [June 5, 2006, 10:14pm UTC](https://www.ruby-forum.com/t/object-troubles-undefined-method/62528/4 "2006-06-05T22:14:35Z")
never mind re-read some more and figured it out. ---
**Author:** ![Paul\_DSKraus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ed655f/32.png) [@Paul\_DSKraus](https://www.ruby-forum.com/u/Paul_DSKraus)\ **Post date:** [June 5, 2006, 10:21pm UTC](https://www.ruby-forum.com/t/object-troubles-undefined-method/62528/5 "2006-06-05T22:21:24Z")
On 6/5/06, Paul D. Kraus [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > ./parse.rb:14:in `incndainvoice': undefined method `+’ for nil:NilClass > (NoMethodError) > from ./parse.rb:31 > from ./parse.rb:20 > ``` > invoices = invoices + 1 > end > def increment_ndainvoice > ndainvoice = ndainvoice + 1 # this is line 14 > end > > ``` > > end You’re problem here is that on line 14, you are actually using a local variable. This is a little tricky, since it’s actually your assignment that is changing the context of the right hand side. What happens is that the parser sees “ndainvoice =” and assumes you’re creating a new local variable called “ndainvoice”; this new local variable then masks the “ndainvoice” method. Since it’s value is nil (the default value of an unassigned-to variable), the effect of the line is: ndainvoice = nil + 1 # ndainvoice is a local variable here In order to get ruby to recognize the assignment as a method call, rather than an assignment to a new local variable, you need to prefix “self.”: self.ndainvoice = ndainvoice + 1 The reference to ndainvoice on the right hand side is correctly interpreted as a method call since there is no local variable of the same name to mask it. Alternatively, you can use the instance variable directly by prefixing an “@” (as you do in initialize): @ndainvoice = @ndainvoice + 1 As a final step, you can also use += to shorten the “a = a + b” pattern: self.ndainvoice += 1 # or @ndainvoice += 1 Incidentally, you have the same problem on line 11. Jacob F.