TypeScript example, for a friend. Explaining types, interfaces, and tuples.

get_parents_example.ts

// Possible `gender` values.
type Gender = 'male' | 'female' | 'other'

// Generic `person` interface.
interface IPerson {
  // Specific string.
  gender: Gender
  
  // Any string.
  name: string

  // `?` means optional.
  mother?: IMother
  father?: IFather
}

// Biological `mother` interface.
interface IMother extends IPerson {
  gender: 'female'
}

// Biological `father` interface.
interface IFather extends IPerson {
  gender: 'male'
}

// Tuple for parents.
type IParents = [IMother, IFather]

// Method to get `[mom, dad]`.
const getParents = (person: IPerson) => {
  // Cast return value as tuple.
  return [person.mother, person.father] as IParents
}

// Define myself.
const Nathan: IPerson = {
  name: 'Nathan',
  gender: 'male',

  mother: {
    name: 'Elise',
    gender: 'female'
  },

  father: {
    name: 'Yoshio',
    gender: 'male'
  }
}

// Alias my parents.
const [myMom, myDad] = getParents(Nathan)

// logs: "Elise".
console.log(myMom.name)

// logs: "Yoshio".
console.log(myDad.name)