From: Johan Veenstra <johan.veenstra@...>
Date: 2006-06-06T05:11:39+09:00
Subject: Re: Object Troubles - undefined method `+'

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>
> 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
> end
>

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