# Recursion and variable scope level

**URL:** <https://www.ruby-forum.com/t/recursion-and-variable-scope-level/152375>\
**Category:** Ruby\
**Created:** [November 3, 2008, 11:07am UTC](https://www.ruby-forum.com/t/recursion-and-variable-scope-level/152375 "2008-11-03T11:07:45Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![scudco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aca169/32.png) [@scudco](https://www.ruby-forum.com/u/scudco)\
**Post date:** [November 3, 2008, 11:07am UTC](https://www.ruby-forum.com/t/recursion-and-variable-scope-level/152375/1 "2008-11-03T11:07:45Z")

</div>

Hi i want to reverse a string and at the same time check if there are  
any spaces using recursion. I can get the string to reverse fine but  
cant detect when theres a space

heres my code

def reverse\_string a\_string, an\_index, spaces  
spaces = true if a\_string[an\_index - 1].chr == ’ ’  
if an\_index == 1  
return a\_string[an\_index - 1].chr  
else  
return a\_string[an\_index - 1].chr + reverse\_string(a\_string,  
an\_index - 1, spaces)  
end

end

and i call it like this

spaces = false  
str = “hello people”  
puts reverse\_string str, str.length, spaces  
puts “Spaces present? #{spaces}”

spaces in the end is set as false though it should be set to true. Is  
this soemthing to do with variable and parameter scope?

---

<div class="post-metadata">

**Author:** ![scudco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aca169/32.png) [@scudco](https://www.ruby-forum.com/u/scudco)\
**Post date:** [November 3, 2008, 11:15am UTC](https://www.ruby-forum.com/t/recursion-and-variable-scope-level/152375/2 "2008-11-03T11:15:49Z")

</div>

oh and im doing this as a way to practice recursion. Using  
string.reverse would of course be the simpler way of doing this.

---

<div class="post-metadata">

**Author:** ![scudco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aca169/32.png) [@scudco](https://www.ruby-forum.com/u/scudco)\
**Post date:** [November 3, 2008, 2:36pm UTC](https://www.ruby-forum.com/t/recursion-and-variable-scope-level/152375/3 "2008-11-03T14:36:03Z")

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Adam A. wrote:

> spaces in the end is set as false though it should be set to true. Is  
> this soemthing to do with variable and parameter scope?

Yes. The ‘spaces’ inside the method definition is a completely separate  
variable to the ‘spaces’ you use outside, since ‘def’ starts a fresh  
scope.

One solution is to return both str and spaces from your function:

def reverse\_string a\_string, an\_index, spaces  
spaces = true if a\_string[an\_index - 1].chr == ’ ’  
if an\_index == 1  
return a\_string[an\_index - 1].chr, spaces  
else  
r1, r2 = reverse\_string(a\_string, an\_index - 1, spaces)  
spaces ||= r2  
return a\_string[an\_index - 1].chr + r1, spaces  
end

end

#and i call it like this

str = “hello people”  
rev, spaces = reverse\_string str, str.length, spaces  
puts rev  
puts “Spaces present? #{spaces}”

Another option is to pass a lambda, which is a function which is called  
whenever a space is detected.

def reverse\_string a\_string, an\_index, spaces  
spaces.call if a\_string[an\_index - 1].chr == ’ ’  
if an\_index == 1  
return a\_string[an\_index - 1].chr  
else  
return a\_string[an\_index - 1].chr + reverse\_string(a\_string,  
an\_index - 1, spaces)  
end

end

#and i call it like this

spaces = false  
str = “hello people”  
puts reverse\_string str, str.length, lambda { spaces=true }  
puts “Spaces present? #{spaces}”

---

<div class="post-metadata">

**Author:** ![scudco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aca169/32.png) [@scudco](https://www.ruby-forum.com/u/scudco)\
**Post date:** [November 3, 2008, 3:04pm UTC](https://www.ruby-forum.com/t/recursion-and-variable-scope-level/152375/4 "2008-11-03T15:04:55Z")

</div>

I dont believe i only just found out that functions can return more than  
one variable in ruby!

How I missed that i dont know.

Thank you very much for your help on that.

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<div class="post-metadata">

**Author:** ![scudco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aca169/32.png) [@scudco](https://www.ruby-forum.com/u/scudco)\
**Post date:** [November 3, 2008, 3:11pm UTC](https://www.ruby-forum.com/t/recursion-and-variable-scope-level/152375/5 "2008-11-03T15:11:39Z")

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Adam A. wrote:

> I dont believe i only just found out that functions can return more than  
> one variable in ruby!
> 
> How I missed that i dont know.
> 
> Thank you very much for your help on that.

No problem.

Really they are just returning an array, and that array may (or may not)  
be split at the receiver.

irb(main):001:0\> def foo; return 1,2; end  
=\> nil  
irb(main):002:0\> x = foo  
=\> [1, 2]  
irb(main):003:0\> x, y = foo  
=\> [1, 2]  
irb(main):004:0\> x  
=\> 1  
irb(main):005:0\> y  
=\> 2  
irb(main):006:0\> def bar; return [1,2]; end  
=\> nil  
irb(main):007:0\> x = bar  
=\> [1, 2]  
irb(main):008:0\> x, y = bar  
=\> [1, 2]  
irb(main):009:0\> x  
=\> 1  
irb(main):010:0\> y  
=\> 2

I believe there’s no difference whether you build an array to return, or  
give multiple values to return.