From: Robert Klemme <shortcutter@...>
Date: 2012-09-11T00:11:53+09:00
Subject: Re: Why does it work? (variable scope)

On Mon, Sep 10, 2012 at 4:57 PM, Iņaki Baz Castillo <ibc@aliax.net> wrote:
> Two similar cases (same behavior):
>
> 1)
> ---------------------
> my_var = 123  if false
>
> puts my_var
> => nil
> ---------------------
>
> 2)
> ---------------------
> if false
>   my_var = 123
> end
>
> puts my_var
> => nil
> ---------------------
>
> Somebody could expect that "puts my_var" should raise "NameError:
> undefined local variable or method `my_var'" in both cases.

The issue with expectations is that sometimes they aren't met. :-)

> So I can understand that in case 1) the Ruby interpreter knows about
> my_var variable since it reads it before checking the "if". But in
> case 2) It seems that my_var variable is known when the script/file is
> loaded since the interpreter will never run into the "if false"
> statement.
>
> Am I right? Thanks a lot.

Mostly.  The variable is known from the lexical position in the code
where it is defined - even if that code is not executed - as you found
out:

> --------------------
> puts "1: defined? my_var: #{(defined? my_var).inspect}"
>
> if false
>   my_var = 123
> end
>
> puts "2: defined? my_var: #{(defined? my_var).inspect}"
>
>
> =>
> 1: defined? my_var: nil
> 2: defined? my_var: "local-variable"
> --------------------

That's also the reason why these behave differently although they seem
to do the same:

$ ruby -e 'if x.nil?; x=123; end; p x'
-e:1:in `<main>': undefined local variable or method `x' for
main:Object (NameError)
$ ruby -e 'x=123 if x.nil?; p x'
123

Kind regards

robert


-- 
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