Reserve

:::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. :::

Reserves enough memory to accommodate a given number of elements

public function reserve(
  int $sz,
): void;

Reserves enough memory for sz elements. If sz is less than or equal to the current capacity of this Map, this method does nothing.

Parameters

• int $sz - The pre-determined size you want for the current Map.

Returns

• void

Examples

This example reserves space for 1000 elements and then fills the Map with 1000 integer keys and values:

const int MAP_SIZE = 1000;

<<__EntryPoint>>
function basic_usage_main(): void {
  $m = Map {};
  $m->reserve(MAP_SIZE);

  for ($i = 0; $i < MAP_SIZE; $i++) {
    $m[$i] = $i * 10;
  }

  \var_dump($m);
}