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map

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 Set containing the values after an operation has been applied to each value in the current Set

public function map<Tu as arraykey>(
  (function(Tv): Tu) $callback,
): Set<Tu>;

Every value in the current Set is affected by a call to map(), unlike filter() where only values that meet a certain criteria are affected.

Guide​

Parameters​

  • (function(Tv): Tu) $callback

Returns​

  • Set<Tu> - a Set containing the values after a user-specified operation is applied.

Examples​

In this example the Set's elements are mapped to the same type (strings):

$s = Set {'red', 'green', 'blue', 'yellow'};

$capitalized = $s->map(fun('strtoupper'));
\var_dump($capitalized);

$shortened = $s->map($color ==> \substr($color, 0, 3));
\var_dump($shortened);

In this example the Set's elements are mapped to a different type (ints):

$s = Set {'red', 'green', 'blue', 'yellow'};

$lengths = $s->map(fun('strlen'));
\var_dump($lengths);