je.rb

class User
  def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
  end

  def full_name(format = nil)
    name = "#{@first_name} #{@last_name}"

    case format.to_sym
    when :csv
      klass_name = Object.const_get("#{format.upcase}Format")
      klass_name.new(name).csv_full_name
    when :xml
      'x' + name
    else
      name
    end
  end
end

class CSVFormat
  def initialize(full_name)
    @full_name = full_name
  end

  def csv_full_name
    "c#{@full_name}"
  end
end

p User.new('User', 'Name').full_name('csv')