This ensures that if a new kind is added to the Animals type and isn't handled in the switch, TypeScript will catch it as a type error at compile time. 🚀

exhaustive-switch-never.ts

// type `never` is great for exhaustive checking, great for exhaustive switch statements
type Bird = {
  kind: 'bird'
  legs: number
  wings: 2
}
type Dog = {
  kind: 'dog'
  legs: number
}
type Fish = {
  kind: 'fish'
  fins: number
}
type Animals = Bird | Dog | Fish

function AnimalAppendages(animal: Animals) {
  switch (animal.kind) {
    case 'bird':
      return animal.legs + animal.wings
    case 'dog':
      return animal.legs
    case 'fish':
      return animal.fins
      break

    default:
      // Exhaustiveness check: If `animal` is ever an unhandled case, TypeScript will throw an error.
      let _: never = animal
      return _
      break
  }
}



type CurrencyOptions = 'EGP' | 'USD' | 'EUR' 

function getRate(rate: CurrencyOptions) {
  switch (rate) {
    case 'EGP':
      return 50
    case 'USD':
      return 1
    case 'EUR':
      return 1.3
    default:
      let _: never = rate
      return _
  }
}