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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 a ConstSet containing the values of the current ConstSet that meet a supplied condition applied to each value

public function filter(
  (function(Tv): bool) $fn,
): ConstSet<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().

Guide​

Parameters​

  • (function(Tv): bool) $fn - The callback containing the condition to apply to the current ConstSet values.

Returns​