# Annoying block variable behaviour!

**URL:** <https://www.ruby-forum.com/t/annoying-block-variable-behaviour/134905>\
**Category:** Ruby\
**Created:** [April 16, 2008, 2:08am UTC](https://www.ruby-forum.com/t/annoying-block-variable-behaviour/134905 "2008-04-16T02:08:07Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\
**Post date:** [April 16, 2008, 2:08am UTC](https://www.ruby-forum.com/t/annoying-block-variable-behaviour/134905/1 "2008-04-16T02:08:07Z")

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Hi, I remember reading somewhere that the Ruby handling of block local  
variables is deprecated and will be fixed, but for now it gives very  
anoying  
behaviour. For example:

This is obvious and correct:

## a)

[1,2,3,4].each { |kk| kk=true }  
=\> [1, 2, 3, 4]

## kk =\> NameError: undefined local variable or method `kk’ for main:Object

But what about this???:

## b)

kk = false  
[1,2,3,4].each { |kk| kk=true }  
=\> [1, 2, 3, 4]

## kk =\>true

So, “kk” is defined as “false” and later in a block it’s “true”, but  
this  
value must not be visible outside the block. In a) it doesn’t occur (so  
OK)  
but in b) is annoying, kk is finally “true” just because in a block it  
was “true” and before it it was defined in top level.

IMHO it makes no sense at all. Is there any explanation for this last  
case?

Thanks for any comment about it.

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**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\
**Post date:** [April 16, 2008, 3:04am UTC](https://www.ruby-forum.com/t/annoying-block-variable-behaviour/134905/2 "2008-04-16T03:04:49Z")

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From: Iñaki Baz C. [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)]

# but in b) is annoying, kk is finally “true” just because in a

# block it was “true” and before it it was defined in top level.

# IMHO it makes no sense at all. Is there any explanation for

# this last case?

the ruby community is divided when it comes to this shadowing behaviour  
of block locals and block params. see the ruby archives.

on your case, ruby1.9 may satisfy

irb(main):005:0\* RUBY\_VERSION  
=\> “1.9.0”  
irb(main):006:0\> [1,2,3,4].each { |kk| kk=true }  
=\> [1, 2, 3, 4]  
irb(main):007:0\> kk  
NameError: undefined local variable or method `kk’ for main:Object

irb(main):008:0\> kk=false  
=\> false  
irb(main):009:0\> [1,2,3,4].each { |kk| kk=true }  
=\> [1, 2, 3, 4]  
irb(main):010:0\> kk  
=\> false

and it comes w warnings too just in case you want to be safe 😉

C:\ruby1.9\bin\>ruby1.9 -we "kk=false; [1,2,3,4].each { |kk| kk=true } "  
-e:1: warning: shadowing outer local variable - kk

kind regards -botp

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<div class="post-metadata">

**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\
**Post date:** [April 16, 2008, 9:58am UTC](https://www.ruby-forum.com/t/annoying-block-variable-behaviour/134905/3 "2008-04-16T09:58:18Z")

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2008/4/16, Peña, Botp [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> the ruby community is divided when it comes to this shadowing behaviour of block locals and block params. see the ruby archives.

Thanks, I’ll look for it.

> irb(main):008:0\> kk=false  
> =\> false  
> irb(main):009:0\> [1,2,3,4].each { |kk| kk=true }  
> =\> [1, 2, 3, 4]  
> irb(main):010:0\> kk  
> =\> false
> 
> and it comes w warnings too just in case you want to be safe 😉

Great to know it, thanks a lot 🙂