nyan.rb

module UserValidator
  module AdministratorContext
    def validate!
      raise "name required" if @name.nil?
    end
  end

  module UserContext
    def validate!
    end
  end
end


class User
  def initialize(name)
    @name = name
  end

  def save!
    validate!
  end

  def validate!
    raise "abstract!"
  end
end

u = User.new(nil)
u.extend UserValidator::AdministratorContext

begin
  u.save!
rescue => e
  p e
end

u = User.new(nil)
u.extend UserValidator::UserContext
u.save!