如何将元组泛型类型映射到联合类型？
type NeededUnionType<T> = T[keyof T]; // Includes all the Array properties values
const value: NeededUnionType<[7, string]> = 2; // This should not be allowed (2 is the tuple length)
预期类型： 7 | string
tuples typescript typescript-generics union-types mapped-types