# Modules setting values to nil in unprocessed conditional blocks?

**URL:** <https://www.ruby-forum.com/t/modules-setting-values-to-nil-in-unprocessed-conditional-blocks/174296>\
**Category:** Ruby\
**Created:** [August 24, 2009, 5:31pm UTC](https://www.ruby-forum.com/t/modules-setting-values-to-nil-in-unprocessed-conditional-blocks/174296 "2009-08-24T17:31:25Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![nate](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e95f7d/32.png) [@nate](https://www.ruby-forum.com/u/nate)\
**Post date:** [August 24, 2009, 5:31pm UTC](https://www.ruby-forum.com/t/modules-setting-values-to-nil-in-unprocessed-conditional-blocks/174296/1 "2009-08-24T17:31:25Z")

</div>

Hi everyone. We’re noticing some strange behavior when including  
modules in classes. It seems that even if a conditional block is  
forced to evaluate as false (and presumably not execute), assignments  
in the conditional block are executed and set to nil. Here is an  
example:

==========================  
module Conundrum  
def riddle  
@riddle ||= ‘mystery’  
end

def riddle=(new\_val)  
puts “Called riddle=”  
@riddle = new\_val  
end  
end

class Test  
include Conundrum

def test  
puts “Before: #{riddle}”  
if true == false  
riddle = ‘solved!’  
end  
puts “After: #{riddle}”  
puts “After class: #{riddle.class}”  
end  
end

# Test.new.test

Note that this prints out:

Before: mystery  
After:  
After class: NilClass

So it would seem that riddle= is not getting called, but yet the  
riddle function now returns nil. Interestingly, this fixes the  
problem:

==========================  
module Conundrum  
def riddle  
@riddle ||= ‘mystery’  
end

def riddle=(new\_val)  
puts “Called riddle=”  
@riddle = new\_val  
end  
end

class Test  
include Conundrum

def test  
puts “Before: #{riddle}”  
if true == false  
@riddle = ‘solved!’  
end  
puts “After: #{riddle}”  
puts “After class: #{riddle.class}”  
end  
end

# Test.new.test

Outputs:

Before: mystery  
After: mystery  
After class: String

Any insights are much appreciated!

-n8

---

<div class="post-metadata">

**Author:** ![nate](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e95f7d/32.png) [@nate](https://www.ruby-forum.com/u/nate)\
**Post date:** [August 24, 2009, 5:59pm UTC](https://www.ruby-forum.com/t/modules-setting-values-to-nil-in-unprocessed-conditional-blocks/174296/2 "2009-08-24T17:59:10Z")

</div>

Nate wrote:

> Hi everyone. We’re noticing some strange behavior when including  
> modules in classes. It seems that even if a conditional block is  
> forced to evaluate as false (and presumably not execute), assignments  
> in the conditional block are executed and set to nil. Here is an  
> example:
> 
> ==========================  
> module Conundrum  
> def riddle  
> @riddle ||= ‘mystery’  
> end
> 
> def riddle=(new\_val)  
> puts “Called riddle=”  
> @riddle = new\_val  
> end  
> end
> 
> class Test  
> include Conundrum
> 
> def test  
> puts “Before: #{riddle}”  
> if true == false

Inside test, self is equal to the Test instance you created here:

> Test.new.test

And this line:

> ```
> puts "Before: #{riddle}"
> 
> ```

is equivalent to:

> ```
> puts "Before: #{self.riddle}"
> 
> ```

However, when ruby parses this line:

> ```
> riddle = 'solved!'
> 
> ```

ruby creates a local variable named riddle. As a result, when you get  
to this statement:

> ```
> puts "After: #{riddle}"
> 
> ```

riddle is no longer equivalent to self.riddle. Instead riddle is just  
riddle; and riddle is a local variable that hasn’t been assigned a  
value. For local variables that exist but have not been assigned a  
value, ruby returns nil for the value of the variable. Then the string  
interpolation calls nil.to\_s which returns a blank string.

---

<div class="post-metadata">

**Author:** ![nate](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e95f7d/32.png) [@nate](https://www.ruby-forum.com/u/nate)\
**Post date:** [August 24, 2009, 6:14pm UTC](https://www.ruby-forum.com/t/modules-setting-values-to-nil-in-unprocessed-conditional-blocks/174296/3 "2009-08-24T18:14:06Z")

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7stud – wrote:

> However, when ruby parses this line:
> 
> > ```
> > riddle = 'solved!'
> > 
> > ```
> 
> ruby creates a local variable named riddle.

Just to clarify: “parse” is different than “execute”. That line will  
never execute, but ruby still parses the code; and it’s when ruby parses  
the code that the local variable riddle is created.

---

<div class="post-metadata">

**Author:** ![nate](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e95f7d/32.png) [@nate](https://www.ruby-forum.com/u/nate)\
**Post date:** [August 24, 2009, 8:51pm UTC](https://www.ruby-forum.com/t/modules-setting-values-to-nil-in-unprocessed-conditional-blocks/174296/4 "2009-08-24T20:51:03Z")

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On Aug 24, 9:14 am, 7stud – [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> ## the code that the local variable riddle is created.
> 
> Posted viahttp://www.ruby-forum.com/.

Clicked “Reply to Author” accidently earlier but meant to give some  
public thanks for your response. So, thanks, appreciate the response  
and the precision you provided in your answer.

- n8 -