From: Phrogz <phrogz@...>
Date: 2010-01-13T07:45:04+09:00
Subject: Re: instance_eval with local variable

On Jan 12, 1:19 pm, Brian Candler <b.cand...@pobox.com> wrote:
> I believe your lambda is bound to the @who in the scope where it was
> defined, you can't dynamically rebind it.

Nope:
  >cat tmp.rb
  @who = "main"
  proc = ->{ p @who }
  proc[]

  bar = Object.new; bar.instance_variable_set :@who, "bar"
  bar.instance_eval( &proc )

  >ruby -v tmp.rb
  ruby 1.9.1p243 (2009-07-16 revision 24175) [i386-mingw32]
  "main"
  "bar"

instance_eval can rebind the proc, but doesn't let you pass arguments
to it.

> I think that what you ask for would lead to very surprising behaviour,
> especially when using blocks:
>
>    @count = 0
>    something.whatever { @who += 1 }

Sure, the concept of a closure is great and 99% of the time should be
preserved. I wasn't asking for my edge-case behavior to be the norm,
but rather trying to figure if it's possible at all.


> > For those interested in second-guessing my approach and coming up with
> > a better way to achieve the same end goal
>
> Perhaps rather than using lambdas, define methods on the object which
> contains the instance variables you're interested in, then call those
> methods (or use method(:name) to get a Method object, which you can pass
> around pretty much like a lambda)

Interesting. Slight downside is the requirement that all plug-ins have
unique method names. Or...hrm, perhaps some insanity involving
define_method on the receiving end of the proc. Thanks for the
suggestion, anyhow.