Type-challenges

type MyPick<T,K extends keyof T> = { [key in K]:T[key] }

type MyReadonly<T> = { readonly [key in keyof T]: T[key] }

type TupleToObject<T extends readonly any[]> = { [value in T[number]]: value }

type First<T extends any[]> = T extends [] ? never  : T[0]

type Length<T extends readonly any[]> = T["length"]