gistfile1.txt

interface Tree {
  branches: number
  species: string
}
interface Vehicle {
  position: number
  speed: number
}
interface Animal {
  legs: number
  speed: number
}

const oak = {
  branches: 10,
  species: 'oak'
}
const willow = {
  branches: 100,
  species: 'willow'
}

const scionIq: Vehicle = {
  position: 0,
  speed: 80
}

function describeTree<K extends keyof Tree>(tree: Tree, key: K) {
  const value = tree[key]
  const message = `The ${key} of this tree is ${value}`
  console.log(message)
}

describeTree<'branches'>(oak, 'branches')

function describeWithSpeed <T extends { speed: number }> (t: T, key: keyof T & string) {
  const value = t[key]
  const message = `The ${key} is ${value}, and the speed is ${t.speed}`
  console.log(message)
}
describeWithSpeed(oak, 'branches')
describeWithSpeed(scionIq, 'position')

const cheetah: Animal = { legs: 4, speed: 90 }
describeWithSpeed(cheetah, 'legs')