config.rb

#
# Super tiny block configuration class, which is
# a great example of nested instance evaluation.
# All using a single class.
#
# Inspired by ...
# http://github.com/ahoward/configuration/blob/master/lib/configuration.rb
#
# Updated: More functionality, less lines of code (gem soon)
#
class ConfigSet

  Index = Hash.new

  def initialize(name)
    @name = name
  end
  
  def yielding(&block)
    @yielding = true
    yield
    @yielding = false
  end

  def self.for(name, &block)
    config = Index[name] ||= ConfigSet.new(name)
    block && config.yielding { config.instance_eval &block }
    config
  end

  def method_missing(name, *args, &block)
    case
    when name.to_s =~ /\=/
      instance_variable_set("@#{name.to_s.gsub(/\=/, '')}", args[0])
    when @yielding
      value = block ? ConfigSet.for(name, &block) : args[0]
      instance_variable_set "@#{name}", value
    when !args[0]
      instance_variable_get "@#{name}"      
    end
  end

end

config_spec.rb

#!/usr/bin/env ruby
require 'rubygems'
require 'bacon'
$:.unshift File.expand_path(File.dirname(__FILE__))
require 'config'

require 'pathname'
$:.unshift Pathname(__FILE__).dirname.expand_path.to_s
require 'spec_helper.rb'

describe ConfigSet, 'storing values' do

  it 'should set values in a block' do
    config = ConfigSet.for :app do
      username 'test123'
      password 'pen159'
    end

    config.username.should.equal 'test123'
  end

  it 'should set values in nested blocks' do
    config = ConfigSet.for :app do
      username 'test123'
      a { ho { sucka 'bitch' } }
    end

    config.a.ho.sucka.should.equal 'bitch'
  end

  it 'should load the same config set twice' do
    ConfigSet.for :app do
      something 'apple'
    end

    ConfigSet.for(:app).something.should.equal 'apple'
  end

  it 'should set a value through its setter' do
    config = ConfigSet.for :app do
      username 'jacob'
    end

    config.username = 'else'
    config.username.should.equal 'else'
  end

  it 'should set a nested value through its setter' do
    config = ConfigSet.for :app do
      user { bacon { name 'jacob' } }
    end

    config.user.bacon.name = 'else'
    config.user.bacon.name.should.equal 'else'
  end

end

puts Bacon.summary_on_exit