# Question on passing blocks

**URL:** <https://www.ruby-forum.com/t/question-on-passing-blocks/141420>\
**Category:** Ruby\
**Created:** [June 25, 2008, 5:45pm UTC](https://www.ruby-forum.com/t/question-on-passing-blocks/141420 "2008-06-25T17:45:55Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\
**Post date:** [June 25, 2008, 5:45pm UTC](https://www.ruby-forum.com/t/question-on-passing-blocks/141420/1 "2008-06-25T17:45:55Z")

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In the code below, a block, { x += 1 } is magically passed to  
thrice ?? or something like that.  
I don’t understand the usage of the “thrice { iterator }” using {}  
and why I can’t make a normal block syntax work. The thrice method  
doesn’t take (normal) parameters, so how does this work?

Ruby, Have you been messing around behind my back?  
Thanks in advance.

def thrice  
yield  
yield  
yield  
end

x = 5  
puts “value of x before: #{x}” # =\> 5  
thrice { x += 1 }  
puts “value of x after: #{x}” # =\> 8

# broken from here down

thrice { |x| x += 1 }

thrice do |x|  
x += 1  
end

---

<div class="post-metadata">

**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\
**Post date:** [June 25, 2008, 6:07pm UTC](https://www.ruby-forum.com/t/question-on-passing-blocks/141420/2 "2008-06-25T18:07:23Z")

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Ruby F. wrote:

> In the code below, a block, { x += 1 } is magically passed to  
> thrice ?? or something like that.  
> I don’t understand the usage of the “thrice { iterator }” using {}  
> and why I can’t make a normal block syntax work. The thrice method  
> doesn’t take (normal) parameters, so how does this work?
> 
> Ruby, Have you been messing around behind my back?  
> Thanks in advance.
> 
> def thrice  
> yield  
> yield  
> yield  
> end
> 
> x = 5  
> puts “value of x before: #{x}” # =\> 5  
> thrice { x += 1 }  
> puts “value of x after: #{x}” # =\> 8
> 
> # broken from here down
> 
> thrice { |x| x += 1 }
> 
> thrice do |x|  
> x += 1  
> end

In the first case, x in the block refers to the x defined outside the  
block. In the 2nd and 3rd cases, you’ve used x as an argument so it  
hides the x outside the block. Any changes you make to x-the-argument  
are lost each time the block exits.

---

<div class="post-metadata">

**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\
**Post date:** [June 25, 2008, 6:11pm UTC](https://www.ruby-forum.com/t/question-on-passing-blocks/141420/3 "2008-06-25T18:11:43Z")

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Ruby F. wrote:

> def thrice  
> yield  
> yield  
> yield  
> end  
> […]
> 
> # broken from here down
> 
> thrice { |x| x += 1 }

You’re passing a block that takes one argument (x) to a method that  
yields  
none. Also: it’s usually not a good idea, to reassign a block argument.  
That  
almost certainly does not do what you want.

HTH,  
Sebastian

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<div class="post-metadata">

**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\
**Post date:** [June 25, 2008, 6:27pm UTC](https://www.ruby-forum.com/t/question-on-passing-blocks/141420/4 "2008-06-25T18:27:34Z")

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Thank you,

I had to get my head around what seems in my mind to be a “backwards  
assignment” in code blocks.  
Oh. that way!

now it makes perfect sense.