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retainWithKey

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.

Alters the current Set so that it only contains the values that meet a supplied condition on its "keys" and values

public function retainWithKey(
  (function(arraykey, Tv): bool) $callback,
): Set<Tv>;

Sets don't have keys, so the Set values are used as the key in the callback.

This method is like filterWithKey(), but mutates the current Set too in addition to returning the current Set.

Future changes made to the current Set ARE reflected in the returned Set, and vice-versa.

Parameters​

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

Returns​