Method missing example

method_missing_example.rb

# Exmaple using method_missing to expose dynamic attributes.
class Foo

  def initialize
    @attrs = {:a => 1, :b => 2}
  end

  def method_missing(method, *args, &block)
    if @attrs.has_key?(method.to_sym)
      send(:[], method, *args)
    else   
      super
    end
  end

  # When you override method_missing, it's good manners to override
  # respond_to? as well.  You can often get away without it.
  def respond_to?(method)
    super || @attrs.has_key?(method.to_sym)
  end

  private

  # This can be public if you want there to be another way to fetch an
  # attribute.  The reason it exists is to get us cheap and easy
  # checking for the number of arguments passed into method_missing.
  def [](attr_name)
    @attrs.fetch(attr_name.to_sym)
  end
   
end

foo = Foo.new
p foo.a                  # => 1
p foo.b                  # => 2   
p foo.respond_to?(:a)    # => true
p foo.respond_to?(:z)    # => false
p foo.a(2)               # => wrong number of arguments
p foo.c                  # => undefined method 'c'