snippet.rb

class FilterableEnumerable
  def initialize(original)
    @original = original
  end
  
  def ==(value)
    @original.select { |v| v == value }
  end
 
  def method_missing(sym, *args, &block)
    @original.select {|v| v.send(sym, *args, &block) }
  end
 
  def respond_to?(sym, include_private = false)
    @original.all? {|v| v.respond_to?(sym, include_private) }
  end
 
end

class NegativeFilterableEnumerable
  def initialize(original)
    @original = original
  end
  
  def ==(value)
    @original.select { |v| v != value }
  end
 
  def method_missing(sym, *args, &block)
    @original.select {|v| ! v.send(sym, *args, &block) }
  end
 
  def respond_to?(sym, include_private = false)
    @original.all? {|v| v.respond_to?(sym, include_private) }
  end
 
end
 
module Enumerable
  def filter
    FilterableEnumerable.new(self)
  end

  def filter_not
    NegativeFilterableEnumerable.new(self)
  end
end
 
 
require 'test/unit'
class TestFilterableEnumerable < Test::Unit::TestCase
  def setup
    @array = (0..10).to_a
  end
 
  def test_gte
    assert_equal [5, 6, 7, 8, 9, 10], @array.filter >= 5
  end
 
  def test_gt
    assert_equal [6, 7, 8, 9, 10], @array.filter > 5
  end
 
  def test_lte
    assert_equal [0, 1, 2, 3, 4], @array.filter < 5
  end
 
  def test_le
    assert_equal [0, 1, 2, 3, 4, 5], @array.filter <= 5
  end
 
  def test_eq
    assert_equal [5], @array.filter == 5
  end
 
  def test_not_eq
    assert_equal [0, 1, 2, 3, 4, 6, 7, 8, 9, 10], @array.filter_not == 5
  end
 
  def test_method_missing
    assert_equal [0], @array.filter.zero?
  end

  def test_not_method_missing
    assert_equal [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], @array.filter_not.zero?
  end
 
  def test_respond_to
    assert @array.filter.respond_to?(:zero?)
  end
 
end