ToImmSet

:::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 an immutable set (ImmSet) with the values of the current Pair

public function toImmSet(): ImmSet<arraykey, mixed>;

Returns

• ImmSet<arraykey,mixed> - an ImmSet with the current values of the current Pair.

Examples

This example shows that converting a Pair to an ImmSet also removes duplicate values:

// This Pair contains 'foo' twice
$p = Pair {'foo', 'foo'};

$imm_set = $p->toImmSet();
\var_dump($imm_set);

This example shows that converting a Pair to an ImmSet will throw a fatal error if the Pair contains a value that's not a string or an int:

$p = Pair {'foo', -1.5};

/* HH_FIXME[4323] Fatal error will be thrown here */
$imm_set = $p->toImmSet();

\var_dump($imm_set);