From: Daniel Lucraft <dan@...>
Date: 2007-07-18T04:41:28+09:00
Subject: Re: Undefined Method confusion - Ruby Newbie (I know it rhym

Kaldrenon wrote:
> Hi all.
> 
> I recently got into challenging myself with some of the tasks over at
> Project Euler (www.projecteuler.net), and while working on the
> solution for one of them (# 14) I came across a Ruby problem. Now, I'm
> pretty sure that this is just a dumbness on my part, but I don't know
> how to fix this problem because I see no differences between my code
> and the examples at http://www.whytheluckystiff.net/ruby/pickaxe/ for
> declaring and calling methods.
> 
> Here's the code (it's tiny so I'll copy the whole thing):
> 
> class Test
>   def series(n,x)
>     if (n == 1)
>       return x
>     elsif (n % 2 == 0 )
>       return sequence(n/2, x + 1)
>     else
>       return sequence(3*n + 1, x + 1)
>     end
>   end
> 
>   max_num = 1
>   max_len = 1
>   for i in 2...1_000_000 do
>     my_len = series(i,1)
>     if (my_len > max_len)
>       max_len = my_len
>       max_num = i
>     end
>   end
>   print max_num , ": chain of length  " , max_len
> end
> 
> The error I'm getting is this:
> undefined method `series' for Test:Class (NoMethodError)
>   from euler14.rb:14:in `each'
> 
> I see no clear reason why I'm getting this error. Can you un-dumb me?
> 
> Thanks in advance,
> Andrew

I enjoy Project Euler too. The error you are getting here is because the 
method 'series' is an instance method, i.e.:
> a = Test.new
> a.series      #=> calls method

> Test.series   #=> gives missing method error

The 'for' loop is executing in the context of the class definition, so 
it is looking for a class method. The error message indicates that it is 
looking for the method on Test:Class.

You can either turn 'series' into a class method:

class Test
  def self.series
  ...

or you can move the for loop out of the class and create a test object:

class Test
  def series
     ...
  end
end

t = Test.new
max_num = 1
max_len = 1
for i in 2...1_000_000 do
  my_len = t.series(i, 1)
  ...

Incidentally, in the code you gave there's no method called 'sequence'. 
Is it possible you meant 'series' there too?

best,
Dan

-- 
Posted via http://www.ruby-forum.com/.