From: Christoph <chr_news@...>
Date: 2002-06-01T14:27:36+09:00
Subject: Re: possible bug: stack dump with <<-String, #{...} and large loops

From: ts decoux@moulon.inra.fr
....
C> def aa(x)
> C>   if x
> C>     eval "p a" # premonition
> C>   end
> C>   a  = 1
> C> end

 > This is normal : when it has compiled the > def it has found a local
 > variable `a', and #eval just retrieve this

It does not really retrieve it - it is just telling Ruby to interpret  ``a''
as
an initialized local variable. Without the `eval part' you would
get a NameError, this difference is really surprising (to me at least;-).
It is at least interesting that running the free form (no method) of the
same Ruby snippet
---
if x
   eval "p a" # no premonition
end
 a  = 1
---
also raises a NameError.

....
> C> def aa
> C>   "#{}"
> C>    eval "a = 1"
> C>    p "#{defined? a}"
> C> end

 > Well, this is a special case (work only with a few version of ruby) where
 > the execution of "#{}" will make all *new* variables dynamic (local
 > in-block). eval "a = 1" in this case create a *new* variable and in this
 > case the variable is dynamic

Thanks for this explanation.

C> def bb
C>   "#{}"
C>   eval "b = 1"
C>   p "#{defined? b}"
C>   b  = 2  # premonition
C> end

 > Same than the first example, `b' was found when ruby has compiled the def
 > #eval just retrieve this variable

so basically it uses the `insight'  (that `b' is a local variable and not
dynamic
variable )  gained at the end of the method body and to reinterpret the
previous lines in that new light?


....

/Christoph