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filter

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 ImmMap containing the values of the current ImmMap that meet a supplied condition

public function filter(
  (function(Tv): bool) $callback,
): ImmMap<Tk, Tv>;

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

The keys associated with the current ImmMap remain unchanged in the returned Map.

Guide​

Parameters​

  • (function(Tv): bool) $callback

Returns​

  • ImmMap<Tk,Tv> - an ImmMap containing the values after a user-specified condition is applied.

Examples​

See Map::filter for usage examples.