AsyncKeyedIterator

:::info[Note] This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information. :::

Allows for the iteration over the keys and values provided by an async function

If an async function returns an AsyncIterator<Tk,Tv>, then you can iterate over the Tk and Tv values returned from that function.

async function countdown(int $start): AsyncIterator<int, string> { ... }

async function use_countdown(): Awaitable<void> {
  $async_iter = countdown(100);
  foreach ($async_gen await as $num => $str) { ... }
}

Guides

• Introduction
• Guidelines

Interface Synopsis

namespace HH;

interface AsyncKeyedIterator implements AsyncIterator<Tv> {...}

Public Methods

• ->next(): Awaitable<?(Tk, Tv)>
  Move the async iterator to the next Awaitable position