NextResult - API reference

API reference › @evolu/common › Result › NextResult

type NextResult<A, E, D> = Result<A, E | Done<D>>;

Defined in: packages/common/src/Result.ts:768

A result for a pull-based protocol with three outcomes.

The consumer requests the next value (e.g. via next()), and the producer responds with one of:

An Ok containing A — produced a value
An Err containing Done — completed normally with a done value
An Err containing E — failed with an error

Inspired by JavaScript's Iterator.next(), which returns { value, done }.

Example

import {
  assertErr,
  assertOk,
  assertType,
  done,
  err,
  ok,
  type NextResult,
  type Typed,
} from "@evolu/common";

const next = (index: number): NextResult<string, ReadFailedError, number> => {
  if (index === 0) return ok("first");
  if (index === 1) return err({ type: "ReadFailed" });
  return err(done(index));
};

interface ReadFailedError extends Typed<"ReadFailed"> {}

const value = next(0);
assertType<NextResult<string, ReadFailedError, number>, typeof value>();
assertOk(value, "first");
assertErr(next(1), { type: "ReadFailed" });
assertErr(next(2), { type: "Done", done: 2 });