Rails - Jan 2006 - asigning values to atributies when source is nil

I want to use something similar to the following:

 @total_price += { product.price <> nil ? product.price : 0.0 }

This fails in rails with a "nil can''t be coerced into Float"
error.
 What is the (most) correct way to do this? 

On a related issue, what is the significance of the value 40 
following "cart.rb" in the trace snippet below?  The entire class 
file is much less than 40 lines long so is this a byte offset?  If 
so, how does one use it to locate the error in the source?
> #{RAILS_ROOT}/app/models/cart.rb:40:in `add_product''
Regards,
Jim

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James B. Byrne wrote:
> I want to use something similar to the following:
> 
>  @total_price += { product.price <> nil ? product.price : 0.0 }
> 
> This fails in rails with a "nil can''t be coerced into
Float" error.
>  What is the (most) correct way to do this? 
   @total_price += product.price.to_f

> On a related issue, what is the significance of the value 40 
> following "cart.rb" in the trace snippet below?  The entire class
> file is much less than 40 lines long so is this a byte offset?  If 
> so, how does one use it to locate the error in the source?
>  
>>#{RAILS_ROOT}/app/models/cart.rb:40:in `add_product''
"@total_price += product.price" is line 40 of
http://media.pragprog.com/titles/rails/code/depot_final/app/models/cart.rb

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We develop, watch us RoR, in numbers too big to ignore.

Mark Reginald James wrote:
>>  What is the (most) correct way to do this? 
> 
>    @total_price += product.price.to_f
> 
> 
Thank you very much. I missed your original reply in the mailing list 
digest which accounts for my delay in responding.

Regards,
Jim

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