# Case/when question

**URL:** <https://www.ruby-forum.com/t/case-when-question/75450>\
**Category:** Ruby\
**Created:** [March 1, 2006, 10:13pm UTC](https://www.ruby-forum.com/t/case-when-question/75450 "2006-03-01T22:13:25Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 1, 2006, 10:13pm UTC](https://www.ruby-forum.com/t/case-when-question/75450/1 "2006-03-01T22:13:25Z")

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I was intrigued by the post that \_why put up a few days/weeks ago  
about using case/when for testing arrays [1]. I thought I’d give it a  
try but I can’t make it work. What am I doing wrong?

irb(main):001:0\> r1 = (0…12).to\_a  
=\> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]  
irb(main):002:0\> r2 = (20…32).to\_a  
=\> [20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32]  
irb(main):003:0\> def foo range  
irb(main):004:1\> case range  
irb(main):005:2\> when \*r1  
irb(main):006:2\> puts “#{range} in r1”  
irb(main):007:2\> when _r2  
irb(main):008:2\> puts “#{range} in r2”  
irb(main):009:2\> else  
irb(main):010:2_ puts “#{range} NOT in any range”  
irb(main):011:2\> end  
irb(main):012:1\> end  
=\> nil  
irb(main):013:0\> foo 3  
NameError: undefined local variable or method `r1' for main:Object from (irb):5:in `foo’  
from (irb):13

This is under OSX:  
ruby 1.8.4 (2005-12-24) [powerpc-darwin8.4.0]

[1] [http://redhanded.hobix.com/bits/wonderOfTheWhenBeFlat.html](http://redhanded.hobix.com/bits/wonderOfTheWhenBeFlat.html)

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 1, 2006, 10:19pm UTC](https://www.ruby-forum.com/t/case-when-question/75450/2 "2006-03-01T22:19:20Z")

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On Mar 1, 2006, at 3:13 PM, removed\_email\_address@domain.invalid wrote:

> irb(main):005:2\> when \*r1  
> from (irb):5:in `foo’  
> from (irb):13

Method definitions, unlike blocks, are not closures and do not have  
access to local variables from the scope where they are defined.  
Move the vars inside the method, or switch them to instance (or  
global) vars and it will work.

Hope that helps.

James Edward G. II

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 1, 2006, 10:21pm UTC](https://www.ruby-forum.com/t/case-when-question/75450/3 "2006-03-01T22:21:05Z")

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On Mar 1, 2006, at 3:13 PM, removed\_email\_address@domain.invalid wrote:

> irb(main):005:2\> when \*r1  
> from (irb):5:in `foo’  
> from (irb):13

Responding to my own email…

I figured it out about 5 minutes after sending. This is purely a  
scope mistake on my part. Variables r1 and r2 are NOT in scope inside  
foo which is exactly what ruby told me.

The fix is to make r1 and r2 into class vars. Change r1 to @r1 and r2  
to @r2 in that example and it works just fine.

Nuby making lots of mistakes!

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 1, 2006, 10:22pm UTC](https://www.ruby-forum.com/t/case-when-question/75450/4 "2006-03-01T22:22:12Z")

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Hi –

On Thu, 2 Mar 2006, removed\_email\_address@domain.invalid wrote:

> irb(main):005:2\> when \*r1  
> from (irb):5:in `foo’  
> from (irb):13

You’ve defined r1 and r2 outside of the scope of the method definition  
block. You need:

def foo(range)  
r1 = (0…12).to\_a  
r2 = … etc

By the way you can also just use the ranges to test inclusion.

David

–  
David A. Black (removed\_email\_address@domain.invalid)  
Ruby Power and Light ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com))

“Ruby for Rails” chapters now available  
from Manning Early Access Program! [Ruby for Rails](http://www.manning.com/books/black)

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 1, 2006, 10:26pm UTC](https://www.ruby-forum.com/t/case-when-question/75450/5 "2006-03-01T22:26:00Z")

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Hi –

On Thu, 2 Mar 2006, removed\_email\_address@domain.invalid wrote:

> > =\> [20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32]  
> > =\> nil
> 
> The fix is to make r1 and r2 into class vars. Change r1 to @r1 and r2 to @r2  
> in that example and it works just fine.

Sort of 🙂 Actually @r1 is an instance variable, not a class  
variable. It’s true that if you do:

@a = 1  
def meth  
puts @a  
end  
meth

you’ll get “1”, but only if you are writing code at the top level of  
the program. If you do this:

class MyClass  
@a = 1  
def meth  
puts @a  
end  
end

```
MyClass.new.meth

```

you won’t because, the two @a’s are different from each other.

Class variables (@@r1) will cross the method-definition divide, but  
they’re somewhat cumbersome… The best thing is to create local  
variables in the scope where you need them (the method definition).

David

–  
David A. Black (removed\_email\_address@domain.invalid)  
Ruby Power and Light ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com))

“Ruby for Rails” chapters now available  
from Manning Early Access Program! [Ruby for Rails](http://www.manning.com/books/black)