From: Rick DeNatale <rick.denatale@...>
Date: 2009-06-16T01:50:24+09:00
Subject: Re: confusion about object method scoping

On Mon, Jun 15, 2009 at 12:31 PM, Christopher Carver<ccarver0@gmail.com> wrote:
> Hello,
>
> I am defining a class.  That class has several methods.  In one of the
> class methods I'm trying to use a previously defined method.  It's
> throwing an exception.  Here's some code that demonstrates my problem.
>  Am I really unable to have a class use some of it's own methods if
> they've already been defined?  Thanks in advance!
>
> class Calculator
>
>  private
>  def add(x,y)
>   x+y
>  end

This defines a method add which any instances of the class Calculator
would have, if you had any, which you don't in this code.
>
>  public
>  def Calculator.factorial(x)
>   result = 0
>
>   (1..x).each { |number|
>     result = add(result,number)
>   }
>
>   result
>  end
>
> end

And this defines a method on the object which is the class called
Calculator. Since Calculator isn't an instance of Calculator it
doesn't have an add method.

Now how to fix it.  One way is

class Calculator
   class < self
      def factorial(x)
         result = 0
         (1..x).each { |number|
         result = add(result,number)
          }
          result
       end

       def add(x, y)
          x + y
       end
    end
end

puts Calculator.factorial(5)

Another way is to actually use an instance of Calculator:

   class Calculator
      def factorial(x)
         result = 0
         (1..x).each { |number|
         result = add(result,number)
          }
          result
       end

       def add(x, y)
          x + y
       end
   end

   puts Calculator.new.factorial(5)

BTW. I've not mentioned until now that your factorial is actually
computing the sum instead of the factorial, because I think that's a
separate issue.

-- 
Rick DeNatale

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