Common gem configuration implementations

gistfile1.rb

class MyGem
  class << self
    attr_accessor :color
  end
  
  def self.configure(&block)
    instance_eval(&block)
  end
end

MyGem.configure do
  self.color = true
end

puts MyGem.color # => true

Object.send(:remove_const, :MyGem)

########################################

class MyGem
  def self.configure
    yield configuration
  end
  
  def self.configuration
    @configuration ||= Configuration.new
  end
  
  class Configuration
    attr_accessor :color
  end
end

MyGem.configure do |config|
  config.color = true
end

puts MyGem.configuration.color # => true

Object.send(:remove_const, :MyGem)

########################################

class MyGem
  def self.configure
    yield configuration
  end
  
  def self.configuration
    @configuration ||= Configuration.new
  end
  
  class Configuration    
    def initialize
      @fields = Fields.new
    end
    
    def fields(&block)
      if block
        @fields.instance_eval(&block)
      else
        @fields.to_pretty
      end
    end
    
    class Fields
      def initialize
        @fields = []
      end
      
      def to_pretty
        {}.tap do |pretty|
          @fields.each do |field|
            pretty[field.name] = {:columns => field.columns}
          end
        end.inspect
      end
      
      def method_missing(sym, *args, &block)
        @fields << Field.new(sym, &block)
      end
      
      class Field
        attr_reader :name, :columns
        
        def initialize(name, &block)
          @name = name
          @block = block
          @columns = []
          
          set_columns
        end
        
        def column(name)
          @columns << name
        end
        
        def set_columns
          instance_eval(&@block) if @block
        end
      end
    end
  end
end

MyGem.configure do |config|
  config.fields do
    dog :canine
    cat :feline
    rat :rodent do
      column :birthdate
      column :food_type
    end
  end
end

puts MyGem.configuration.fields # => 
  # {
  #   :dog => { :columns => [] },
  #   :cat => { :columns => [] },
  #   :rat => { :columns => [:birthdate, :food_type] }
  # }