type Assignment = { kind: "assign"; key: string; value: string };
type Flag = { kind: "flag"; key: string };
type Token = Assignment | Flag | { kind: "comment"; text: string };
const tokenize = (line: string): Token => {Use utility conditional types to parse and narrow a small input grammar.
type Nested = Promise<Promise<Promise<string>>>;
type Flat = Awaited<Nested>;
export async function loadUser(): Promise<{ id: string; name: string }> {
return { id: "1", name: "Ada" };Unwrap Promise<Promise<Promise<T>>> down to T in one step, the way await does at runtime, using TypeScript's built-in recursive helper.
export type DeepPartial<T> = T extends readonly unknown[]
? T
: T extends object
? { [K in keyof T]?: DeepPartial<T[K]> }
: T;Make every property optional at every nesting level, for patch-style updates, without touching arrays element by element.
type AsyncReturnType<Fn extends (...args: never[]) => unknown> = Fn extends (
...args: never[]
) => Promise<infer R>
? R
: Fn extends (...args: never[]) => infer RBuild a return-type extractor that also unwraps the Promise, so async and sync functions land on the same resolved type.
type ParamNames<Path extends string> = Path extends `${string}:${infer Param}/${infer Rest}`
? Param | ParamNames<Rest>
: Path extends `${string}:${infer Param}`
? Param
: never;Extract :param names out of a route string at the type level, so a route's caller must supply exactly the params that route needs.