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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 a ConstMap containing the values of the current ConstMap that meet a supplied condition applied to its keys and values

public function filterWithKey(
  (function(Tk, Tv): bool) $fn,
): ConstMap<Tk, Tv>;

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

The keys associated with the current ConstMap remain unchanged in the returned ConstMap; the keys will be used in the filtering process only.

Parameters​

  • (function(Tk, Tv): bool) $fn - The callback containing the condition to apply to the current ConstMap keys and values.

Returns​

  • ConstMap<Tk,Tv> - a ConstMap containing the values after a user-specified condition is applied to the keys and values of the current ConstMap.