David Kimura PRO said over 3 years ago on User Notifications :
  ruby object and instantiating it in the comment controller create action

def create
  @comment = Comment.new(comment_params)
  if @comment.save
    CommentNotifier.call(@comment)
    ...
  else
    ...
  end
end

From there, you can make the Comment Notifier have guard clauses, do any checks and pass in any other additional parameters needed. (like passing in the current user to have a guard clause return unless current_user == comment.user) to prevent the current user getting a notification if they reply to their own comment.