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retain

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.

Ensures that this Map contains only keys/values for which the specified callback returns true when passed the value

public function retain(
  mixed $callback,
): HH\Map;

Parameters​

  • mixed $callback

Returns​

  • object