Type Lookup

[antfu]

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Detailed solution/guide is not required, but be sure the challenge is solvable.

Please follow the template and fill the info. A PR will be auto-generated and always reflect on your changes.

Info

Basic info of your challenge questions,

difficulty: medium # medium / hard / extreme
title: Type Lookup
tags: union, map

Question

Sometimes, you may want to lookup for a type in a union to by their attributes.

In this challenge, I would like to have get the couponing type by searching for the common type field in the union Cat | Dog. In other words, I will expect to get Dog for LookUp<Dog | Cat, 'dog'> and Cat for LookUp<Dog | Cat, 'cat'> in the following example.

interface Cat {
  type: 'cat'
  breeds: 'Abyssinian' | 'Shorthair' | 'Curl' | 'Bengal'
}

interface Dog {
  type: 'dog'
  breeds: 'Hound' | 'Brittany' | 'Bulldog' | 'Boxer'
  color: 'brown' | 'white' | 'black'
}

const MyDog = LookUp<Cat | Dog, 'dog'> // expected to be `Dog`

Template

This is the template for challengers to start the coding. Basically, you just need to change the name of your generic/function and leave to implementation any.

type LookUp<U, T> = any

Test Cases

Provide some test cases for your challenge, you can use some utils from @type-challenges/utils for asserting.

import { Equal, Expect } from '@type-challenges/utils'

interface Cat {
  type: 'cat'
  breeds: 'Abyssinian' | 'Shorthair' | 'Curl' | 'Bengal'
}

interface Dog {
  type: 'dog'
  breeds: 'Hound' | 'Brittany' | 'Bulldog' | 'Boxer'
  color: 'brown' | 'white' | 'black'
}

type Animal = Cat | Dog

type cases = [
  Expect<Equal<LookUp<Animal, 'dog'>, Dog>>,
  Expect<Equal<LookUp<Animal, 'cat'>, Cat>>,
]

[github-actions]

#63 - Pull Request updated.