snippet.rb

# Spawned from this thread: http://rubyflow.com/items/1990

module Enumerable
  # Wraps an enumerable in an easy interface for selecting subsets. Comparison
  # and method calls are supported.
  #
  #  [0, 1, 2, 3].filter > 1        # => [2, 3]
  #  [0, 1, 2, 3].filter.zero?      # => [0]
  # 
  # Warning: Do not use this with the != operator, use filter_not instead.
  #
  #  [0, 1, 2, 3].filter != 1       # => false
  def filter
    FilterableEnumerable.new(self)
  end
 
  # Wraps an enumerable in an easy interface for selecting subsets with a
  # negative comparison. Comparison and method calls are supported.
  #
  #  [0, 1, 2, 3].filter_not > 1    # => [0, 1]
  #  [0, 1, 2, 3].filter_not.zero?  # => [1, 2, 3]
  #   
  # Warning: Do not use this with the != operator, use filter instead.
  def filter_not
    FilterableEnumerable.new(self, true)
  end
end

class FilterableEnumerable
  def initialize(original, negate = false)
    @original = original
    @negate = negate
  end
  
  def ==(value)
    @original.select { |v| (v == value) ^ @negate }
  end
 
  def method_missing(sym, *args, &block)
    @original.select { |v| v.send(sym, *args, &block) ^ @negate }
  end
 
  def respond_to?(sym, include_private = false)
    @original.all? { |v| v.respond_to?(sym, include_private) }
  end
end
 
 
 
require 'test/unit'
class TestFilterableEnumerable < Test::Unit::TestCase
  def setup
    @enumerable = 0..10
  end
 
  def test_gte
    assert_equal [5, 6, 7, 8, 9, 10], @enumerable.filter >= 5
  end
 
  def test_gt
    assert_equal [6, 7, 8, 9, 10], @enumerable.filter > 5
  end
 
  def test_lte
    assert_equal [0, 1, 2, 3, 4], @enumerable.filter < 5
  end
 
  def test_le
    assert_equal [0, 1, 2, 3, 4, 5], @enumerable.filter <= 5
  end
 
  def test_eq
    assert_equal [5], @enumerable.filter == 5
  end
 
  def test_not_eq
    assert_equal [0, 1, 2, 3, 4, 6, 7, 8, 9, 10], @enumerable.filter_not == 5
  end
 
  def test_method_missing
    assert_equal [0], @enumerable.filter.zero?
  end
 
  def test_not_method_missing
    assert_equal [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], @enumerable.filter_not.zero?
  end
 
  def test_respond_to
    assert @enumerable.filter.respond_to?(:zero?)
  end
end