Ruby interpreter magically assigns unreferenced variables?

Asked Nov 05 '14 at 16:11

Active Nov 05 '14 at 16:11

Viewed 17 times

$ irb
irb(main):001:0> foo
NameError: undefined local variable or method `foo' for main:Object
  from (irb):1
  from /Users/justinwiley/.rbenv/versions/2.1.2/bin/irb:11:in `<main>'

So far so good, 'foo' is undefined.

irb(main):002:0> if false
irb(main):003:1> foo = 1
irb(main):004:1> end
=> nil

foo should still be undefined, but...

irb(main):005:0> foo
=> nil

Now it exists in the symbol table? Since the logic in the if branch should never be reached, I would assume foo should remain undefined, instead of suddenly being nil?

asked Nov 05 '14 at 16:11

Allyl Isocyanate

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Have a look at this answer: http://stackoverflow.com/a/1335890/163640 – eugen Nov 05 '14 at 16:15
@eugen: I was looking for a good reference answer. Thanks for finding it. :) – Sergio Tulentsev Nov 05 '14 at 16:18
Thanks eugen. I'm trying to understand why Ruby has this behaviour? Is this intentional or a side effect? – Allyl Isocyanate Nov 05 '14 at 16:19
@juwiley: that's just how ruby works. local vars are created at parse time. Weird, but we have to live with it. – Sergio Tulentsev Nov 05 '14 at 16:20
I dont think "thats just the way it is" is a good answer in computer science. Heres a link to an answer with more details on why this behavior exists: http://stackoverflow.com/questions/12706664/interpretation-as-a-local-variable-overrides-method-name – Allyl Isocyanate Nov 05 '14 at 16:39
@juwiley: you passed the test. :) – Sergio Tulentsev Nov 07 '14 at 08:16

Ruby interpreter magically assigns unreferenced variables?

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