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comp.lang.ruby

Undefined Method confusion - Ruby Newbie (I know it rhymes, don't hurt me

Kaldrenon

7/17/2007 7:24:00 PM

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/rub... 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
3 Answers

Alex LeDonne

7/17/2007 7:40:00 PM

0

On 7/17/07, Kaldrenon <kaldrenon@gmail.com> 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/rub... 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

Andrew,

You've created an instance method, but you're calling a class method.

Try defining a class method with:

def self.series(n,x)

instead.

Also, did you notice that you're returning sequence(), rather than series()? :)

-Alex

Daniel Lucraft

7/17/2007 7:41:00 PM

0

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/rub... 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-....

Sebastian Hungerecker

7/17/2007 7:44:00 PM

0

Kaldrenon wrote:
> 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?

You define series as an instance method, but you try to invoke it as a class
method. If you do

class Bla
def blubb() end
end
x=Bla.new

there will be a x.blubb but no Bla.blubb.
If you want a Bla.blubb you have to define it with "def self.blubb".
Also given the fact that you never create an instance of your class, you don't
actually need to define a class.


--
Ist so, weil ist so
Bleibt so, weil war so