[ruby-core:24435] Re: lvar_propagate

Hi,

On Sat, Jul 18, 2009 at 10:06 AM, Yukihiro Matsumoto<[e-mail]> wr=
ote:
> Hi,
>
> In message "Re: [ruby-core:24421] lvar_propagate"
> =A0 =A0on Sat, 18 Jul 2009 15:17:36 +0900, Yehuda Katz <[e-mail]>=
 writes:
>
> |Very good keynote today. I enjoyed looking at some of the new features y=
ou
> |are playing around with. I was very existed about lvar_propagate, and am
> |hoping I can convince you to give it another chance :)
> |
> |Here's why: In my ideal world, blocks behave transparently to the end us=
er.
> |There would be no difference between:
>
> In my ideal world, there's no implicit block-local variable, just flat
> to innermost scope making construct, e.g. def, class, module etc. =A0And
> when one want block-local variables, he need to declare them by using
> block local variable list in the block parameter part (|a; b c|), or
> by using :=3D assignment from block_local_vars_eq patch stack, which was
> also in the keynote.
>
> =A0100.times do |x|
> =A0 =A0v1 =3D x
> =A0 =A0v2 :=3D x
> =A0 =A0...
> =A0end
> =A0p v1 =A0# local variable; no block scope
> =A0p v2 =A0# name error; out of scope
>
> In real world, It would cause serious compatibility problem. =A0That's
> the very reason I made up far more complex local variable propagation.
>
> Shugo came to me today telling me he made a patch to realize flat
> local variable scope that can be enabled by magic comment, so that
>
> =A0100.times do |x|
> =A0 =A0v1 =3D x
> =A0 =A0...
> =A0end
> =A0p v2 =A0# name error; out of scope
>
> But if there's a magic comment
>
> =A0# -*- nested-local-variables: false -*-
> =A0100.times do |x|
> =A0 =A0v1 =3D x
> =A0 =A0...
> =A0end
> =A0p v2 =A0# local variable; no block scope
>
> I have not yet have any conclusion about the idea, but eventual
> migration using magic comment may be realistic (or not). =A0I am not
> sure which is the best way from:
>
> =A0* keeping as they are. =A0no compatibility issue.
> =A0* local variable propagation. =A0complex, but works for most of the
> =A0 =A0cases. =A0little (if any) compatibility issue.
> =A0* flat local variable scope, unless explicitly declared. =A0has
> =A0 =A0compatibility issue. =A0need migration path.

I am a bit confused. What would the following snippets do if lvar
propagation is implemented?

# Snippet1
0.times { x =3D 42 } # never called
x # nil or NameError?

# Snippet2
def foo
  proc { x =3D 42 } # created but called later
end
def bar
  foo.call
  x # 42 or NameError?
end
bar

Thanks,
Laurent