Ruby Advent Calender 2022

my_yaml_loader.rb

require 'yaml'
require 'delegate'

module MyNodeExtension
  refine Psych::Nodes::Node do
    def mapping_key?
      @mapping_key
    end

    attr_writer :mapping_key
  end
end

using MyNodeExtension

class MyTreeBuilder < Psych::TreeBuilder
  def scalar(value, anchor, tag, plain, quoted, style)
    node = super
    node.mapping_key = @last.mapping? && @last.children.size.odd?
    node
  end
end

class MyValue < SimpleDelegator
  def initialize(value, line, column)
    super(value)
    @line = line
    @column = column
  end

  attr_reader :line, :column
end

class MyVisitor < Psych::Visitors::ToRuby
  def accept(node)
    object = super
    if node.mapping? || node.sequence? || (node.scalar? && !node.mapping_key?)
      MyValue.new(object, node.start_line + 1, node.start_column + 1)
    else
      object
    end
  end
end

def my_yaml_load(yaml)
  parser = Psych::Parser.new(MyTreeBuilder.new)
  parser.parse(yaml)
  ast = parser.handler.root.children[0]

  visitor = MyVisitor.create
  visitor.accept(ast)
end

yaml = <<~YAML
  children:
    - name: Kanta
      age: 5
    - name: Kaede
      age: 1
YAML

obj = my_yaml_load(yaml)

p [obj.line, obj.column]
p [obj['children'].line, obj['children'].column]
p [obj['children'][0].line, obj['children'][0].column]
p [obj['children'][0]['name'].line, obj['children'][0]['name'].column]
p [obj['children'][0]['age'].line, obj['children'][0]['age'].column]
p [obj['children'][1].line, obj['children'][1].column]
p [obj['children'][1]['name'].line, obj['children'][1]['name'].column]
p [obj['children'][1]['age'].line, obj['children'][1]['age'].column]