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filterWithKey

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.

Returns an ImmSet containing the values of the current ImmSet that meet a supplied condition applied to its "keys" and values

public function filterWithKey(
  (function(arraykey, Tv): bool) $callback,
): ImmSet<Tv>;

Since ImmSets don't have keys, the callback uses the values as the keys as well.

Only values that meet a certain criteria are affected by a call to filterWithKey(), while all values are affected by a call to mapWithKey().

Parameters​

  • (function(arraykey, Tv): bool) $callback

Returns​

  • ImmSet<Tv> - an ImmSet containing the values after a user-specified condition is applied to the values of the current ImmSet.

Examples​

See Set::filterWithKey for usage examples.