離散数学読書会（＠2012-02-12）

myset.rb

class MySet < Array
  def and(set)
    self.map{ |elem| elem if set.include? elem }.compact
  end
  def or(set)
    result = self
    set.each{ |elem| result << elem unless result.include? elem }
    result
  end
  def minus(set)
    self.map{ |elem| elem unless set.include? elem }.compact
  end
  def include?(elem)
    self.each { |e| return true if e == elem }
    nil
  end
end

describe MySet do
  describe "and" do
    it { MySet.new([1, 2, 3]).and(MySet.new([2, 3])).should == [2, 3] }
  end
  describe "or" do
    it { MySet.new([1, 2, 3]).or(MySet.new([2, 4, 5])).should == [1, 2, 3, 4, 5] }
  end
  describe "minus" do
    it { MySet.new([1, 2, 3]).minus(MySet.new([2, 4, 5])).should == [1, 3] }
  end
  describe "include?" do
    it { MySet.new([1, 2, 3]).include?(2).should be_true }
  end
end