From: kturing@... (kate turing)
Date: 2002-01-27T18:13:59+09:00
Subject: Re: "friend" alternative in Ruby?

Stared at the ceiling for a while and came up with this 
approach. Make Foo.initialize "return" a block that calls 
Foo.privateThing. You can only get such a block  (precluding 
__send__, etc.) by being the one that called Foo.new. 

This is a bit more of a mess than using built-in-to-the-language
access control, of course. But it's sort of cute.

k.


class FooMgr
  def initialize
    @privateBlocks = Hash.new
  end
  def createFoo r
    Foo.new r do |x|
      @privateBlocks[r] = x
    end
  end
  def frobulate r
    @privateBlocks[r].call
  end
end

class Foo
  def initialize r
    @r = r
    yield Proc.new {privateThing}
  end
  private
  def privateThing
    puts "private #{@r}"
  end
end

resources = ['r1', 'r2', 'r3']
fm = FooMgr.new

#create a bunch of Foo objects
foos = resources.collect { |r| fm.createFoo r }

#frobulate them, indirectly calling Foo.privateThing
resources.each { |r| fm.frobulate r }

# This will throw a NameError, as desired
foos[0].privateThing