# Why do these two code blocks have different behavior?

**URL:** <https://www.ruby-forum.com/t/why-do-these-two-code-blocks-have-different-behavior/103399>\
**Category:** Ruby\
**Created:** [May 5, 2007, 6:45am UTC](https://www.ruby-forum.com/t/why-do-these-two-code-blocks-have-different-behavior/103399 "2007-05-05T06:45:19Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![yuricake](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/71c47a/32.png) [@yuricake](https://www.ruby-forum.com/u/yuricake)\
**Post date:** [May 5, 2007, 6:45am UTC](https://www.ruby-forum.com/t/why-do-these-two-code-blocks-have-different-behavior/103399/1 "2007-05-05T06:45:19Z")

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I am not a total newbie in ruby, but I am still hazy on how things  
like blocks, proc objects and contexts work under the covers. I have  
experience with Lisp lambdas, so feel free to get technical.

My question is - why do the following two functions have different  
behavior?

require “pp”

@@a = [1, 2, 3]

def q1  
@@a.inject(0) {|sum, x|  
pp x  
return sum + x  
}  
end

def q2  
@@a.inject(0) {|sum, x|  
pp x  
sum + x  
}  
end

---

<div class="post-metadata">

**Author:** ![yuricake](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/71c47a/32.png) [@yuricake](https://www.ruby-forum.com/u/yuricake)\
**Post date:** [May 5, 2007, 7:05am UTC](https://www.ruby-forum.com/t/why-do-these-two-code-blocks-have-different-behavior/103399/2 "2007-05-05T07:05:21Z")

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On May 5, 2007, at 12:45 AM, yuricake wrote:

> return sum + x  
> }  
> end
> 
> def q2  
> @@a.inject(0) {|sum, x|  
> pp x  
> sum + x  
> }  
> end

Because the return statement terminates the method q1 and not the  
block that is associated with the call to inject. You are effectively  
bailing out of inject on the first iteration.

In q2, when control runs off the end of the block, control is returned  
to inject, which can continue with its iterations.

Gary W.

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<div class="post-metadata">

**Author:** ![yuricake](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/71c47a/32.png) [@yuricake](https://www.ruby-forum.com/u/yuricake)\
**Post date:** [May 5, 2007, 7:07am UTC](https://www.ruby-forum.com/t/why-do-these-two-code-blocks-have-different-behavior/103399/3 "2007-05-05T07:07:21Z")

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The return statement is causing an early break.  
it doesn’t do what you think it does (what it does in other languages)  
The desired behavior is in q2.  
Ruby automatically returns the result of the last statement in the  
block.  
Also, a clue that you’re thinking in another language is the curly  
braces.  
Ruby style is to use curly braces for one-liners and do-end for multi-  
line blocks.

---

<div class="post-metadata">

**Author:** ![yuricake](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/71c47a/32.png) [@yuricake](https://www.ruby-forum.com/u/yuricake)\
**Post date:** [May 5, 2007, 12:04pm UTC](https://www.ruby-forum.com/t/why-do-these-two-code-blocks-have-different-behavior/103399/4 "2007-05-05T12:04:36Z")

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> def q1  
> @@a.inject(0) {|sum, x|  
> pp x  
> return sum + x  
> }  
> end  
> I’ll add one thing to the other’s explanations: ‘next’ does what you  
> thought ‘return’ was doing: it terminates the block, returning the value  
> given as argument

def q1  
@@a.inject(0) do |sum, x|  
pp x  
next sum + x  
end  
end

will also work

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<div class="post-metadata">

**Author:** ![yuricake](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/71c47a/32.png) [@yuricake](https://www.ruby-forum.com/u/yuricake)\
**Post date:** [May 5, 2007, 7:08am UTC](https://www.ruby-forum.com/t/why-do-these-two-code-blocks-have-different-behavior/103399/5 "2007-05-05T07:08:21Z")

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On 5/5/07, yuricake [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> def q1  
> @@a.inject(0) {|sum, x|  
> pp x  
> return sum + x  
> this return will jump out of the method altogether. So the method will  
> print x once, and then return sum + x, that is 0 + 1 = 1  
> }  
> end
> 
> def q2  
> @@a.inject(0) {|sum, x|  
> pp x  
> sum + x  
> }  
> end

in this case, there’s no return to interrupt the inject loop, so the  
sum will be calculated properly and return value from the method will  
be the return value of inject, i.e. the sum 6.