summary
- With named types like interface, tree definitions, etc. could be done before.
- Since 3.7, type alias can be done in some cases.
- But we can’t define recurrently in the way we wanted to do it this time.
- You can’t even make it an INTERFACE.
- Resolution Create natural numbers with TypeScript types.
I just wanted to add… ts
type N0 = [];
type succ<N> = [any, N];
type N1 = succ<N0>
type N2 = succ<N1>
type N3 = succ<N2>
type pred<N> = N extends [any, infer R] ? R : never;
type NEQUAL<Na, Nb> = Na extends Nb ? any : never;
type testNEQUAL = NEQUAL<pred<N2>, succ<N0>> // any
type add<Na, Nb> = Nb extends N0 ? Na : add<succ<Na>, pred<Nb>>
// Type alias 'add' circularly references itself.https://stackoverflow.com/questions/36966444/how-to-create-a-circularly-referenced-type-in-typescript https://github.com/microsoft/TypeScript/pull/33050 TypeScript In 3.7 ts
type ValueOrArray<T> = T | Array<ValueOrArray<T>>; // OK
type ValueOrArray<T> = T | ValueOrArray<Array<T>>; // NGts
type add<Na, Nb> = Nb extends N0 ? Na : add2<Na, Nb>;
interface add2<Na, Nb> extends add<succ<Na>, pred<Nb>> { }; // NG
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