From: Robert Klemme <bob.news@...>
Date: 2003-01-31T23:25:30+09:00
Subject: Re: Local variables & blocks


"Yukihiro Matsumoto" <matz@ruby-lang.org> schrieb im Newsbeitrag
news:1043933439.835669.17626.nullmailer@picachu.netlab.jp...
> Hi,
>
> In message "Re: Local variables & blocks"
>     on 03/01/30, "Robert Klemme" <bob.news@gmx.net> writes:
>
> |Just to make sure: From what I read in this thread there are quite some
> |situations which could be problematic with exporting a variable from a
> |block to its enclosing scope. Are all these situations properly
regarded?
> |
> |I still feel a unwary about this change...
>
> Describe your feeling and ideas.  This is why I post.  What kind of
> situations do you think this change does not cover properly?

(i) It's that the control is reversed. Currently the enclosing scope
defines variables that are visible in the block. This is common behavior
for most languages and people are used to it.

(ii) I don't find it too hard to declare a variable outside the block in
order to be able to use it inside and after the block. So I personally
would not gain much.

(iii) Binding is deferred to execution time. Currently I don't fully
oversee all implications of this. Here are some thoughts: It could const
performance. Runtime errors vs. compile time erros. Errors might be hard to
track down: think of someone creating a Proc instance, handing that to a
method that invokes another method etc. until it arrives in the method that
finally uses it. Maybe the block comes from a different module. Now I
suddenly get errors because the block creates variables in my method's
scope, instead of beeing restricted to the creator's scope.

With the change, will it be possible to do something like this a bit
artifical example?

class C
  def initialize
    @has_run = false
  end

  def createProc
    Proc.new { @has_run = true }
  end

  def has_run?
    has_run
  end
end

c = C.new
p = c.createProc

c.has_run?

a = []
a.each { p.call }
c.has_run?

a << 1 << 2
a.each { p.call }
c.has_run?


Regards

    robert