memeby.rb

module Kernel
  def an(value)
    Thingy.new(value)
  end

  def none
    Nothing.new
  end
end

class Thingy < Struct.new(:value)
  def has_value?
    true
  end
end

class Nothing
  include Enumerable
  def has_value?
    false
  end

  def each
  end
end

describe "with value" do
  it "knows an object" do
    an(1).value.should == 1
  end

  it "has a value" do
    an(1).should have_value
  end

  it "enumerates an object" do
    an(1).each do |value|
      value.should == 1
    end
  end

  it "can be mapped" do
    an(1).map {|x| x}.should == [1]
  end
end

describe "without value" do
  it "doesn't enumerate no object" do
    none.each do |value|
      raise
    end
  end

  it "knows no object" do
    none.should_not have_value
  end

  it "maps to empty array" do
    none.map {|x| x}.should == []
  end
end