How to use double quoted a string node

yaml_preserved_string_quote.rb

class YAMLPreservedStringQuote
    def initialize(*doublequoted_nodes)
      @doublequoted_nodes = doublequoted_nodes
    end

    def load(str)
      ast = YAML.parse_stream(StringIO.new(str))

      ast.grep(Psych::Nodes::Mapping).each do |node|
        node.children.each_slice(2) do |key, value|
          next unless @doublequoted_nodes.include?(key.value)

          if value.is_a?(Psych::Nodes::Sequence)
            value.children.each(&method(:double_quote!))
          else
            double_quote!(value)
          end
        end
      end

      ast
    end

    private

    def double_quote!(node)
      node.plain  = false
      node.quoted = true
      node.style  = Psych::Nodes::Scalar::DOUBLE_QUOTED
    end
  end