gistfile1.txt

/*
type Input <T> = {
  data: T | string
}

type PremiumInput <T> = Input<T> & {
  price: number
}
*/

interface Input <T = boolean> {
  data: T | string
}

interface PremiumInput <T extends string | number> extends Input<T> {
  price: number
}

const alpha: Input<200 | 201> = { data: 200 }
const beta: Input<400 | 404> = { data: 400 }
const gamma: Input = { data: true }
const delta: PremiumInput<number> = { data: 'hello', price: 100 }

function annotate <T> (data: T) {
  return {
    data,
    date: new Date()
  }
}

const annotatedString = annotate('hello')
const annotatedNumber = annotate(100)

function formatNumber (value: number) {
  console.log(value.toFixed(2))
}

formatString(annotatedString.data)
formatNumber(annotatedNumber.data)

interface Artist {
  name: string
  medium: string
  works: string[]
}

type ArtistKey = keyof Artist
type ArtistValue = Artist[ArtistKey]

const dorothy: Artist = {
  name: 'Dorothy Parker',
  medium: 'plays',
  works: []
}

function describeArtist <T extends ArtistKey> (artist: Artist, key: T) {
  const value = artist[key]
  console.log(`The ${key} of ${artist.name} is ${value}`)
  return value
}
const medium = describeArtist(dorothy, 'medium') // The medium of Dorothy Parker is plays
const works = describeArtist(dorothy, 'works')

function formatString (value: string){
  console.log(value.toLowerCase())
}
function formatArray (value: string[]) {
  console.log(value.join(', '))
}

formatString(medium)
formatArray(works)