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AsyncIterator

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 values provided by an async function

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

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

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

Guides​

Interface Synopsis​

namespace HH;

interface AsyncIterator {...}

Public Methods​