HashBuilder allows you to build a Hash in Ruby similar to Builder with some enhancements

hash_builder.rb

# Allows you to build a Hash in a fashion very similar to Builder. Example:
# Fork of https://gist.github.com/360506 by BrentD with some enhancements
#
#   HashBuilder.build! do |h|
#     h.name "Nilesh"
#     h.skill "Ruby"
#     h.skill "Rails" # multiple calls of the same method will collect the values in an array
#     h.location "Udaipur, India" do # If a block is given, first argument will be set as value for :name
#       h.location do
#         h.longitude 24.57
#         h.latitude 73.69
#     end
#   end
#
# produces:
#
# {:name=>"Nilesh", :skill=>["Ruby", "Rails"], :location=>{:name=>"Udaipur, India", :location=>{:longitude=>24.57, :latitude=>73.69}}}

class HashBuilder
  instance_methods.each { |m| undef_method m unless m =~ /(^__|^nil\?$|^send$|^object_id$)/ }
  
  def initialize
    @hash = {}
    @target = @hash
  end
  
  def self.build!
    builder = HashBuilder.new
    yield builder
    builder.to_h
  end
    
  def to_h
    @hash
  end
  
  def inspect
    to_h.inspect
  end
  
  def attr!(key, value=nil)
    if block_given?
      parent = @target
      @target = {}
      @target[:name] = value if value
      yield # the block may not be able to override "name" because Class#name exists but takes no argument
      parent[key] = @target
      @target = parent
    else
      if @target.keys.include?(key)
        @target[key] = [@target[key]].flatten + [value]
      else
        @target[key] = value
      end
    end
    @hash
  end
  
  def method_missing(key, *args, &block)
    attr!(key, args.first, &block) # If block_given?, first argument will be taken as the value of :name. Others will be discarded.
  end
end

class Hash
  unless method_defined?(:build!)
    def build!(&block)
      ::HashBuilder.build!(&block)
    end
  end
end