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: ast_node_class_map.rb
    path of file: ./repos/reek/lib/reek/ast
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

require_relative 'node'
require_relative 'sexp_extensions'

module Reek
  module AST
    # Maps AST node types to sublasses of ASTNode extended with the relevant
    # utili
    
      def extension_map
        @extension_map ||=
          begin
            assoc = SexpExtensions.constants.map do |const|
              [
                const.to_s.sub(/Node$/, '').downcase.to_sym,
                SexpExtensions.const_get(const)
              ]
            end
            assoc.to_h
          end