remove_constant

# File activesupport/lib/active_support/dependencies.rb, line 740
    def remove_constant(const) #:nodoc:
      # Normalize ::Foo, ::Object::Foo, Object::Foo, Object::Object::Foo, etc. as Foo.
      normalized = const.to_s.delete_prefix("::")
      normalized.sub!(/\A(Object::)+/, "")

      constants = normalized.split("::")
      to_remove = constants.pop

      # Remove the file path from the loaded list.
      file_path = search_for_file(const.underscore)
      if file_path
        expanded = File.expand_path(file_path)
        expanded.delete_suffix!(".rb")
        loaded.delete(expanded)
      end

      if constants.empty?
        parent = Object
      else
        # This method is robust to non-reachable constants.
        #
        # Non-reachable constants may be passed if some of the parents were
        # autoloaded and already removed. It is easier to do a sanity check
        # here than require the caller to be clever. We check the parent
        # rather than the very const argument because we do not want to
        # trigger Kernel#autoloads, see the comment below.
        parent_name = constants.join("::")
        return unless qualified_const_defined?(parent_name)
        parent = constantize(parent_name)
      end

      # In an autoloaded user.rb like this
      #
      #   autoload :Foo, 'foo'
      #
      #   class User < ActiveRecord::Base
      #   end
      #
      # we correctly register "Foo" as being autoloaded. But if the app does
      # not use the "Foo" constant we need to be careful not to trigger
      # loading "foo.rb" ourselves. While #const_defined? and #const_get? do
      # require the file, #autoload? and #remove_const don't.
      #
      # We are going to remove the constant nonetheless ---which exists as
      # far as Ruby is concerned--- because if the user removes the macro
      # call from a class or module that were not autoloaded, as in the
      # example above with Object, accessing to that constant must err.
      unless parent.autoload?(to_remove)
        begin
          constantized = parent.const_get(to_remove, false)
        rescue NameError
          # The constant is no longer reachable, just skip it.
          return
        else
          constantized.before_remove_const if constantized.respond_to?(:before_remove_const)
        end
      end

      begin
        parent.instance_eval { remove_const to_remove }
      rescue NameError
        # The constant is no longer reachable, just skip it.
      end
    end