Ruby break expression acting weird

Question

require 'csv'

i = 0
CSV.foreach("survdata.csv", headers: true) do |row|
  puts row
  i++
  if i > 1 then
    break
  end
end

This looks so simple, and yet it doesn't run. Can you see why I am getting:

/mydev/surveyresult/surveyresult.rb:11: void value expression

FWIW: There's no `++` operator in ruby: http://stackoverflow.com/questions/3717519/no-increment-operator-in-ruby — orde, Mar 29 '16 at 16:20
Oh is my face red! Thanks @stackoverflow! (I've been teaching Java the last 3 months and my ruby mental database has been corrupted!!!) — pitosalas, Mar 29 '16 at 16:29
@pitosalas If you are really a professor (or even if you are actually not), please be politically correct. — sawa, Mar 29 '16 at 16:38

score 1 · Answer 1 · edited Mar 29 '16 at 17:33

1

Ruby doesn't have an increment operator the last time I looked.

In place of

i++

do

i += 1

edited Mar 29 '16 at 17:33

the Tin Man

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answered Mar 29 '16 at 16:24

SteveTurczyn

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score 1 · Accepted Answer · edited May 23 '17 at 12:16

1

Ruby does not support i++ syntax as a shortcut to i+=1. See "Why doesn't Ruby support i++ or i-- (increment/decrement operators)?" for more information why.

You can fix your code like this:

require 'csv'

i = 0
CSV.foreach("survdata.csv", headers: true) do |row|
  puts row
  i = i+1
  if i > 1 then
    break
  end
end

More information on the error message (thanks sawa):

Ruby does actually support i++ syntax. If it is followed by x, it is interpreted as unary operator + applied to x, whose result passed as an argument to i+. In your example, if i > 1 then; break; end does not return any value, hence the error message "void value expression".

edited May 23 '17 at 12:16

Community

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answered Mar 29 '16 at 16:25

babgyy

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To be strict, your answer is wrong. If Ruby did not support such construct syntactically, then it would raise a syntax error, but it doesn't. It does support `i++` syntax. If it is followed by `x`, it is interpreted as unary operator `+` applied to `x`, whose result passed as an argument to `i+`. – sawa Mar 29 '16 at 16:27
Fair strict point. However there was no `x` here, can we agree to say it won't work as expected by the author ? – babgyy Mar 29 '16 at 16:34
`x` in this case is `if i > 1 then; break; end`. Furthermore, this does not answer the question why the OP is getting "void value expression". Along the lines of your answer, can you answer why it did not raise a syntax error? – sawa Mar 29 '16 at 16:35

score 0 · Answer 3 · answered Mar 29 '16 at 16:21

0

Yes. It is because the:

if i > 1 then
  break
end

part breaks, which does not have a return value (within the code block in question). And you cannot apply the unary operator +@ to something that lacks a value, nor can i.+ take the return value of such as an argument.

answered Mar 29 '16 at 16:21

sawa

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Why was this down voted? Despite the accepted answer has a clearer explanation this one is also correct. – xuuso Jun 30 '16 at 18:02

Ruby break expression acting weird

3 Answers3