BFE.dev solution for TypeScript puzzle
4. implement Record<K, V>

Looking at the description, we need to somehow create an object out of the union type.

This is perfect use case of Mapped Type.

type MyRecord<K, V> = {
   [P in K]: V
}

But only string, symbol and number can be used as object key, so we need to add constraint by extends

type MyRecord<K extends string | number | symbol, V> = {
   [P in K]: V
}

A useful trick is that we can use keyof any to shorten the restraint, since keyof any would return all the possible types of object keys.

type MyRecord<K extends keyof any, V> = {
   [P in K]: V
}