gistfile1.rb

hash_field :body
hash_field :type { self.class.to_s }
hash_fields :body,
            :title,
            :version => "1.2.0",
            :type => -> { self.class.to_s }

def self.hash_field (key, value=nil, &block)
  if block_given?
    value = block
  elsif value.nil?
    value = key
  end

  @hash_fields[key] = value
end

def self.hash_fields (*keys)
  keys.each do |key|
    if key.is_a? Hash
      @hash_fields.merge!(key)
    else
      @hash_fields[key] = key
    end
  end
end

def to_hash
  hash = {}
  self.class.hash_fields.each do |key, value|
    if value.respond_to? :call
      hash[key] = value.call
    elsif self.respond_to? value
      hash[key] = send(value)
    else
      hash[key] = value
    end
  end
  hash
end