Invariant Callback Register

:::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. :::

Pass a function that will be called if any invariant fails

namespace HH;

function invariant_callback_register(
  (function(string, mixed ...): void) $callback,
): void;

The callback will be called with all the invariant parameters after the condition.

Parameters

• (function(string, mixed ...): void) $callback - The function that will be called if your invariant fails.

Returns

• void