From: pharrington <xenogenesis@...>
Date: 2010-01-13T05:20:04+09:00
Subject: Re: instance_eval with local variable

On Jan 12, 3:04 pm, pharrington <xenogene...@gmail.com> wrote:
> On Jan 12, 2:57 pm, Phrogz <phr...@mac.com> wrote:
>
>
>
>
>
> > On Jan 12, 12:23 pm, Phrogz <phr...@mac.com> wrote:
> > [snip]> For those interested in second-guessing my approach and coming up with
> > > a better way to achieve the same end goal
>
> > FWIW, there is a workaround I've come up with. Instead of trying to
> > evaluate the proc in the scope and access instance variables directly,
> > I can pass the object to the proc and work from its public interface.
> > My original code is thus changed:
>
> > > def self.process_snippets( html )
> > >   @snippets.inject(html){ |h,(regexp,handler)| h.gsub( regexp, &handler ) }
>
> > def self.process_snippets( html, bundle )
> >   @snippets.inject(html){ |h,(r,proc)| h.gsub(r){ |s| proc
> > [s,bundle] } }
>
> > >   # Mark $$foo$$ as glossary items.
> > >   DocuBot.handle_snippet /\$\$\w[^$]+\$\$/ do |match|
> > >     # TODO: look up the glossary term in the bundle's glossary
> > >     # and insert appropriate text, or flag a new glossary term
> > >     "<span class='glossary'>#{match[2..-3]}</span>"
> > >   end
>
> > DocuBot.handle_snippet /\$\$\w[^$]+\$\$/ do |match, bundle|
> >   term = match[2..-3]
> >   defn = bundle.glossary[term]
> >   "<span class='glossary' title='#{defn}'>#{term}</span>"
> > end
>
> > I'm thus unblocked in my endeavors, but still interested in the
> > metaprogramming needed to accomplish my original goal. I was actually
> > a little surprised that instance_eval doesn't take an arbitrary number
> > of arguments in the block form and splat them along to the block's
> > parameters.
>
> Well, I'm not sure if this is the particular sort of nastiness you're
> looking for, but.... defining a new method with the proc works..
>
> xeno@amrita:~/projects  $ cat nasty.rb
> obj = Object.new
> obj.instance_variable_set :@who, "foo"
> @who = "main"
> holla = lambda {|str| p @who, str}
>
> class << obj
>   def eigen
>     class << self; self; end
>   end
> end
>
> obj.eigen.send(:define_method, :holla, &holla)
> obj.holla "horrah"
> xeno@amrita:~/projects  $ ruby nasty.rb
> "foo"
> "horrah"

FWIW, I tend to only uses procs when metaprogramming when I want their
closure properties. Otherwise, pretty much everything else Ruby offers
is a better fit.