From: transfire@...
Date: 2006-07-16T10:59:53+09:00
Subject: Module#private_filter: critique of dynamic method visibility

The following fancy function does some pretty delicate handling of
method visibility. And as such I would really like to get some extra
eyes on it. I wonder, is it worth it? Can it be improved? Is there a
whole better way of dealing? Etc.

The idea is to be able to define a pattern of methods that will be
granted public visibility, while all others are kept private, even when
new methods are added dynamically to Kernel or Object.

I'm currently using it like so:

  class OpenObject < Hash
     private_filter //
     ....
    def method_missing(sym,*args)
       ....
    end
  end

Thanks,
T.


class Module

  STANDARD_FILTER =
/(\?$|^(__|object_|instance_)|^(send|inspect|dup|clone|null|\W+)$)/

  @@private_filters = {}

  def private_filter( *filter )
    return @@private_filters[self] if filter.empty?
    filter.collect! do |f|
      if f == //
        STANDARD_FILTER
      elsif Regexp === f
        f
      else
        f.to_s
      end
    end
    @@private_filters[self] = filter
    public_instance_methods.each do |name|
      case name.to_s
      when *filter
#puts "public #{name}"
      else
#puts "private #{name}"
        private name
      end
    end
    filter
  end

  #
  #

  def self.filter(name)
    @@private_filters.each do |base, filter|
      case name.to_s
      when *base.private_filter
      else
        base.send(:private,name)
      end
    end
  end

end

# Since Ruby is very dynamic, methods added to the ancestors of a class
# after private_filter is defined will show up in the list of public
methods.
# We handle this by defining  hooks in Object, Kernel and Module that
will
# hide any defined.

module Kernel
  class << self
    madded = method(:method_added)
    define_method(:method_added) do |name|
      r = madded.call(name)
      return r if self != Kernel
      Module.filter(name)
      r
    end
  end
end

# See Kernel callback.

class Object
  class << self
    madded = method(:method_added)
    define_method(:method_added) do |name|
      r = madded.call(name)
      return r if self != Object
      Module.filter(name)
      r
    end
  end
end



#  _____         _
# |_   _|__  ___| |_
#   | |/ _ \/ __| __|
#   | |  __/\__ \ |_
#   |_|\___||___/\__|
#

=begin test

  require 'test/unit'

  class TestMethodFilter1 < Test::Unit::TestCase

    class X
      private_filter //
      def foo ; end
      def method_missing(name,*args)
        name
      end
    end

    def test_1_01
      x = X.new
      assert_equal( :class, x.class )
    end

    def test_1_02
      x = X.new
      assert_not_equal( :object_id, x.object_id )
    end

    def test_1_02
      x = X.new
      assert( x.respond_to?(:foo) )
    end

  end

=end