# Undefined method '\<' for nil:NilClasse

**URL:** <https://www.ruby-forum.com/t/undefined-method-for-nil-nilclasse/132333>\
**Category:** Ruby\
**Created:** [March 19, 2008, 7:39am UTC](https://www.ruby-forum.com/t/undefined-method-for-nil-nilclasse/132333 "2008-03-19T07:39:07Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![robyonrails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@robyonrails](https://www.ruby-forum.com/u/robyonrails)\
**Post date:** [March 19, 2008, 7:39am UTC](https://www.ruby-forum.com/t/undefined-method-for-nil-nilclasse/132333/1 "2008-03-19T07:39:07Z")

</div>

This is the code:  
class StringScanner  
@str = “”  
@kounter = 0  
def initialize(str)  
@str = str  
end  
def scan(arg)  
res = @str.scan(arg)  
return nil unless @kounter\<res.length  
@kounter=@kounter+1  
res[@kounter-1]  
end  
end

str = “Watch how I soar!”  
ss = StringScanner.new(str)  
loop do  
word = ss.scan(/\w+/) # Grab a word at a time  
break if word.nil?  
puts word  
sep = ss.scan(/\W+/) # Grab next non-word piece  
break if sep.nil?  
end

And this is the result:  
C:/Documents and Settings/Roby/Desktop/Apps/Ruby/prova2.rb:9:in `scan': undefined method`\<’ for nil:NilClass (NoMethodError)  
from C:/Documents and  
Settings/Roby/Desktop/Apps/Ruby/prova2.rb:18  
from C:/Documents and  
Settings/Roby/Desktop/Apps/Ruby/prova2.rb:17:in `loop’  
from C:/Documents and  
Settings/Roby/Desktop/Apps/Ruby/prova2.rb:17

Help.

---

<div class="post-metadata">

**Author:** ![robyonrails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@robyonrails](https://www.ruby-forum.com/u/robyonrails)\
**Post date:** [March 19, 2008, 7:59am UTC](https://www.ruby-forum.com/t/undefined-method-for-nil-nilclasse/132333/2 "2008-03-19T07:59:46Z")

</div>

You have to initialize instance members inside the initialize  
function, or another function that’s called after instantiation.  
That’s why @kounter is nil. Try putting @kounter=0 inside #initialize

HTH  
MT

On Wed, Mar 19, 2008 at 2:38 PM, Roberto C.

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**Author:** ![robyonrails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@robyonrails](https://www.ruby-forum.com/u/robyonrails)\
**Post date:** [March 19, 2008, 10:55am UTC](https://www.ruby-forum.com/t/undefined-method-for-nil-nilclasse/132333/3 "2008-03-19T10:55:52Z")

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Roberto C. wrote:

> ```
> @kounter=@kounter+1
> 
> ```
> 
> sep = ss.scan(/\W+/) # Grab next non-word piece  
> from C:/Documents and  
> Settings/Roby/Desktop/Apps/Ruby/prova2.rb:17
> 
> Help.

I’m not sure I understand Ruby at all…, but @kounter.class is  
‘NilClass’.

Graham

---

<div class="post-metadata">

**Author:** ![robyonrails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@robyonrails](https://www.ruby-forum.com/u/robyonrails)\
**Post date:** [March 19, 2008, 11:28am UTC](https://www.ruby-forum.com/t/undefined-method-for-nil-nilclasse/132333/4 "2008-03-19T11:28:29Z")

</div>

Roberto C. wrote:

> ```
> @kounter=@kounter+1
> 
> ```
> 
> sep = ss.scan(/\W+/) # Grab next non-word piece  
> from C:/Documents and  
> Settings/Roby/Desktop/Apps/Ruby/prova2.rb:17
> 
> Help.

The probblem is in the initializing. If you explicitly initialize  
@kounter in the initialize method then it knows it’s a Fixnum.

Graham

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<div class="post-metadata">

**Author:** ![robyonrails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@robyonrails](https://www.ruby-forum.com/u/robyonrails)\
**Post date:** [March 19, 2008, 11:50am UTC](https://www.ruby-forum.com/t/undefined-method-for-nil-nilclasse/132333/5 "2008-03-19T11:50:57Z")

</div>

On 3/19/08, Slark [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> The probblem is in the initializing. If you explicitly initialize  
> @kounter in the initialize method then it knows it’s a Fixnum.

Variables aren’t typed in Ruby, nor are they declared. A variable  
isn’t a particular class, it refers to an object, and the reference  
can change over the life of the program.

@a = 1 #@a is now a fix num  
@a = @a \* 1.2 # And now it’s a float  
@a = @a.to\_s # And now it’s a String

–  
Rick DeNatale

My blog on Ruby  
[http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)

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**Author:** ![robyonrails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@robyonrails](https://www.ruby-forum.com/u/robyonrails)\
**Post date:** [March 19, 2008, 11:47am UTC](https://www.ruby-forum.com/t/undefined-method-for-nil-nilclasse/132333/6 "2008-03-19T11:47:25Z")

</div>

On 3/19/08, Roberto C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> This is the code:  
> class StringScanner  
> @str = “”  
> @kounter = 0

Since the previous two lines are inside a class context rather than  
inside an instance method, they define two class instance variables,  
i.e. they are instance variables of the class object named  
StringScanner.

These two variables are never actually used in the rest of the code,  
much as it might seem to an untrained eye.

> def initialize(str)  
> @str = str

This creates an instance variable for the INSTANCE of StringScanner  
being initialized, this is an entirely different variable than the  
@str we saw before.

> end  
> def scan(arg)  
> res = @str.scan(arg)  
> return nil unless @kounter\<res.length

Again @kounter is an instance variable associated with a particular  
StringScanner object, it is NOT the previously seen @kounter.

> puts word  
> sep = ss.scan(/\W+/) # Grab next non-word piece  
> break if sep.nil?  
> end

Now even if you straighten out the two variables, you are going around  
Robin Hood’s barn to accomplish what can be easily done with:

“Watch how I soar!”.scan(/\w+/).each {|word| puts word}

or perhaps

puts “Watch how I soar!”.scan(/\w+/).join(“\n”)

–  
Rick DeNatale

My blog on Ruby  
[http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)

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**Author:** ![robyonrails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@robyonrails](https://www.ruby-forum.com/u/robyonrails)\
**Post date:** [March 19, 2008, 1:58pm UTC](https://www.ruby-forum.com/t/undefined-method-for-nil-nilclasse/132333/7 "2008-03-19T13:58:34Z")

</div>

Roberto C. wrote:

> ```
> @kounter=@kounter+1
> 
> ```
> 
> sep = ss.scan(/\W+/) # Grab next non-word piece  
> from C:/Documents and  
> Settings/Roby/Desktop/Apps/Ruby/prova2.rb:17
> 
> Help.

A simple way to understand how scoping (and naming convention) is  
working in ruby is to try the following 3 examples and note their  
output/errors:

1…  
class C  
str = “Hello”  
def look  
puts str.class  
end  
end  
c = C.new  
c.look

2…  
class C  
@str = “Hello”  
def look  
puts @str.class  
end  
end  
c = C.new  
c.look

3…  
class C  
@@str = “Hello”  
def look  
puts @@str.class  
end  
end  
c = C.new  
c.look

Graham

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<div class="post-metadata">

**Author:** ![robyonrails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@robyonrails](https://www.ruby-forum.com/u/robyonrails)\
**Post date:** [March 19, 2008, 2:16pm UTC](https://www.ruby-forum.com/t/undefined-method-for-nil-nilclasse/132333/8 "2008-03-19T14:16:49Z")

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Oki guys. I understand.  
Thank you!