example.rb

:foo / :bar           # => [:foo, :bar]
:foo / :bar / :fizz   # => [:foo, :bar, :fizz]
:foo / :bar / :foo    # => [:foo, :bar]
:foo / :bar / :fizz / :bizz   # => [:foo, :bar, :fizz, :bizz]

the code.rb

class Symbol
  class SymbolSet < Array
    def /(sym)
      SymbolSet.new([self, sym].flatten.uniq)
    end
  end
  
  def /(sym)
    SymbolSet.new([self, sym])
  end
end

if __FILE__ == $0
  %w(rubygems spec).each { |lib| require lib }

  describe Symbol, "/" do
    it "returns array" do
      result = :foo / :bar
      result.should == [:foo, :bar]
    end
  
    describe "SymbolSet" do
      it "allows chaining" do
        result = :foo / :bar / :fizz / :bizz
        result.should == [:foo, :bar, :fizz, :bizz]
      end
      
      it "is unique" do
        result = :foo / :bar / :foo
        result.should == [:foo, :bar]
      end
    end
  end
end