From: dblack@... (David Alan Black)
Date: 2003-01-06T09:59:12+09:00
Subject: Re: Accessing a block's "receiver"

Hi --

Martin DeMello <martindemello@yahoo.com> wrote in message news:<KuYR9.86244$na.2370717@news2.calgary.shaw.ca>...
> I was writing the following piece of code:
> 
> class String
> def title_case(exceptions = [])
>   exclude = %w(a an the some and but or not for) + exceptions 
>   split(/\b/).map_with_index {|w, i| 
>   (exclude.include?(w) or 
>     ((i>1) && self[i-1] == "'" && self[i-2] =~ /w/)) ? w : w.capitalize
> }.join.capitalize
> end
> end
> 
> when I realised that 'self' was not what I wanted, since it belongs to
> the block definition scope. What I want is a way to get at the anonymous
> self.split object to which the block is passed - i.e. a variable recv,
> analogous to self, that gets set when a block is yielded to or a proc is
> called.
> 
> As it stands, I have to introduce a separate variable, b, just so I can
> say b = split(/\b\); b.map_with_index {|w,i| ... b[i] ...} - this
> *feels* like it should be unnecessary. What would be nice would be for
> 'yield args' to implicitly be 'yield self, args', proc.call(*args) be
> proc.call(self, args) and {|args| ...} be {|recv, args| }.
> 
> Good idea? Bad idea? Disastrously bad idea? :)

Does "disaster" include causing all Ruby code to stop working? :-)

Even leaving that aside, it doesn't appeal to me.  In exchange for a few cases 
where you'd have to refactor (as above), you'd have thousands of cases 
where you'd see:

  obj.meth {|discard_me,a,b| ...}

You could use instance_eval:

class String
  def title_case(exclude = [])
    exclude.concat(%w(a an the some and but or not for))
    split(/\b/).instance_eval {
      map_with_index {|w, i|
        (exclude.include?(w) or
         ((i>1) && self[i-1] == "'" && self[i-2] =~ /w/)) ? w : w.capitalize }
    }.join
  end
end

(Includes some left-over tweakings from playing around -- just ignore
those :-)


David Black
dblack@candle.superlink.net

(posting from Google... soon to resubscribe to ruby-talk after being out
of town)