Ruby Config Hierarchy Class

config_hierarchy_classes.rb

#!/usr/bin/env ruby

# This file demonstrates a simple experiment to make a hierarchy of config classes
# where each class can simply define a hash of config values which augment/override
# those of it's parent class. Each class uses class methods to access the config
# values by name. In addition to the config hash, each class can define custom
# class methods that combine/format config values, even if those values are actually
# defined in an ancestor or descendant class.

class BaseConfig
  ########################################
  # Config This Class
  ########################################
  def initialize
    @values = {
      :base_url => "http://www.example.com",
      :path     => "api"
    }
  end
  

  ########################################
  # Common Base Class Helpers
  ########################################
  def self.url
    "#{self.base_url}/#{self.path}"
  end
  

  ########################################
  # Base Class Magic
  ########################################
  class << self
    attr_accessor :instance
  end

  def method_missing(method, *params)
    msym = method.to_sym
    if @values.has_key?(msym)
      return @values[msym]
    else
      self.class.ancestors[1].send(method, *params)
    end
  end

  def self.method_missing(method, *params)
    self.instance ||= self.new
    self.instance.send(method, *params)
  end
end

######################################################################
# Subclasses (these just config their values)
######################################################################

class ServerConfig < BaseConfig
  def initialize
    @values = {
      :port => "9090"
    }
  end
end

class LocalConfig < BaseConfig
  def initialize
    @values = {
      :state => "Washington"
    }
  end
end

# Note two levels of class inheritance and the crazy way of writing
# it to try to move everything out of sight but the config values.
class MicroConfig < LocalConfig; def initialize; @values = {
      
  :city => "Kirkland",

  # Note it can override a parent's config.
  :path => "KirkApi"

}; end; end


# Test to prove it.
puts "#{BaseConfig.url}"
puts "#{ServerConfig.url}/#{ServerConfig.port}"
puts "#{LocalConfig.url}/#{LocalConfig.state}"
puts "#{MicroConfig.url}/#{MicroConfig.state}/#{MicroConfig.city}"