From: Christoph <chr_news@...>
Date: 2002-06-06T22:12:12+09:00
Subject: Re: eval and local variable

"ts" <decoux@moulon.inra.fr> wrote in message
....
>  Not for me, this mean that

since you understand whats going on anyway;-)

>
>    * at compile type no local variable with the name 'foo' was defined
>    * at run time, no method with  the name `foo' was defined

The difference of compile and runtime is blurred (in my mind at least;-)
and may explain the difficulties some people (including myself) have in
understanding visibility rules of local variables.

For example, I find it curious that Ruby raises a NameError when a
variable name is used before being  declared, even so the interpreter
seems to have complete knowledge of all local_variable (that are
and will be) declared in the current scope.

---
p local_variables

begin
x = (eval "foo").nil?   # doesn't raises a NameError since `foo'  is
declared
                                   # in the rescue clause
p foo                           # raises a NameError since `foo' is not
declared yet.
rescue => mes
  p mes
  foo = 'bar'
end

p x,foo
p local_variables

begin
 x = eval "foo"
 p foo
rescue => mes
  p mes
  foo = 'bar'
end

p x,foo

# ["x", "mes", "foo"]
# #<NameError: undefined local variable or method `foo' for
#<Object:0x100fb0a8>>
# true
# "bar"
---

and for good measure the eval version ...

---
eval %{
p local_variables

begin
 x = (eval "foo").nil?  # already raises a NameError ...
 p foo
rescue => mes
  p mes
  foo = 'bar'
 end

p x,foo  # curiously this does not raise an `x' NameError

}

# results in
# []
# #<NameError: (eval):1: undefined local variable or method `foo' for
#<Object:0x100fb0a8>>
# nil
# "bar"
---

/Christoph