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hphp/hack/manual/apis/Interfaces/ConstMap/map.md

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:::info[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 after an operation has been applied to each value in the current ConstMap

Hack
public function map<Tu>(
  (function(Tv): Tu) $fn,
): ConstMap<Tk, Tu>;

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

The keys will remain unchanged from the current ConstMap to the returned ConstMap.

Guide

Parameters

  • (function(Tv): Tu) $fn - The callback containing the operation to apply to the current ConstMap values.

Returns

  • ConstMap<Tk,Tu> - a ConstMap containing key/value pairs after a user-specified operation is applied.
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