Casting flow types

castFlow.js

type QuestionType = {
  answers: string;
};

type PostType = {
  comments: string;
};

type ActivityItemType = {
  type: 'question' | 'post';
} & (PostType | QuestionType);

function getComments(post: PostType) {
  return post.comments
}

function getAnswers(question: QuestionType) {
  return question.answers
}

function getContent(activityItem: ActivityItemType) {
  switch (activityItem.type) {
    case 'post':
      return getComments(((activityItem: any): PostType));
    case 'question':
      return getAnswers(((activityItem: any): QuestionType));
    default:
      return null;
  }
}