Array Map

:::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. :::

array_map previously had it's signature rewritten based on the arity of the call, to match runtime behaviors including:

• Preserving the input container type
• Allowing for N args and accepting a function of the same arity

function array_map<Tk as arraykey, Tin, Tout>(
  (function(Tin): Tout) $callback,
  KeyedContainer<Tk, Tin> $arr,
): KeyedContainer<Tk, Tout>;

This runtime behavior still exists but this function is deprecated in favor of HSL functions like Vec\map or Dict\map.

Parameters

• (function(Tin): Tout) $callback
• KeyedContainer<Tk,Tin> $arr

Returns

• KeyedContainer<Tk,Tout>