shapes-capa.rb

require 'objspace'
require 'json'

class Foo
  class_eval <<~RUBY
    def initialize
      #{21.times.map { |i| "@attr_#{i} = #{i}" }.join("\n")}
    end
  RUBY

  def define_ivars(num, offset: 0, suffix: '')
    num.times do |i|
      instance_variable_set(:"@attr_#{i + offset + 1}#{suffix}", i + offset + 1)
    end
  end
end

2.times do |iter|
  puts "=" * 40
  obj = Foo.new
  p obj

  if iter == 1
    obj.define_ivars(7, suffix: "extra")
    obj.remove_instance_variable(:@attr_20)
    obj.define_ivars(9, suffix: "extra")
  end

  shapes = ObjectSpace.dump_shapes(output: :string)

  $shapes = shapes.lines.map { |l| JSON.parse(l) }.each_with_object({}) { |s, h| h[s["id"]] = s }
  def shape_ancestors(s)
    if s["parent_id"]
      shape_ancestors($shapes[s["parent_id"]])
    end
    p s
  end

  puts
  shape_id = JSON.parse(ObjectSpace.dump(obj))["shape_id"]
  shape_ancestors($shapes[shape_id])
  puts

  puts ObjectSpace.dump(obj)
end