You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: ancestor_graph.rb
    path of file: ./repos/rbs/lib/rbs
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

module RBS
  class AncestorGraph
    InstanceNode = _ 
    
    def build_ancestors(node, ancestors)
      ancestors.each_ancestor do |ancestor|
        case ancestor
        when Definition::Ancestor::Instance
          register(child: node, parent: InstanceNode.new(type_name: ancestor.name))
        when Definition::Ancestor::Singleton
          register(child: node, parent: SingletonNode.new(type_name: ancestor.name))
        end
      end