I have tuple of Maybe
types:
class Maybe<T>{ }
type MaybeTuple = [Maybe<string>, Maybe<number>, Maybe<boolean>];
and I want to turn this into a tuple of types:
type TupleIWant = [string, number, boolean];
so I tried this:
type ExtractTypes<T> = T extends Maybe<infer MaybeTypes>[] ? MaybeTypes : never;
type TypesArray = ExtractTypes<MaybeTuple>; // string | number | boolean NOT [string, number, boolean]
Which doesn't work :-(
I get (string | number | boolean)[]
rather than the tuple I want: [string, number, boolean]
Is what I want to do currently possible?
You'll need to use a mapped tuple type, which is supported in TypeScript 3.1.
You can make a mapped type that has properties 0
, 1
, 2
and length
of the correct types, like this:
class Maybe<T> {}
type MaybeTuple = [Maybe<string>, Maybe<number>, Maybe<boolean>];
type MaybeType<T> = T extends Maybe<infer MaybeType> ? MaybeType : never;
type MaybeTypes<Tuple extends [...any[]]> = {
[Index in keyof Tuple]: MaybeType<Tuple[Index]>;
} & {length: Tuple['length']};
let extractedTypes: MaybeTypes<MaybeTuple> = ['hello', 3, true];
If you're using an older version of typescript, you can use an unreleased version of TypeScript, or as a workaround, you can write a conditional type to match against tuples as long as you think you are likely to have, e.g., like this.