Typescript: type never

https://stackoverflow.com/questions/37910669/what-is-the-difference-between-never-and-void-in-typescript

function expression 과  function declaration 에서 void 와 never의 차이

https://stackoverflow.com/questions/40251524/typescript-never-type-inference

never를 이용한 타입 안정성 예시

https://basarat.gitbooks.io/typescript/docs/types/discriminated-unions.html