Slice

:::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 subset of the current ImmVector starting from a given key up to, but not including, the element at the provided length from the starting key

public function slice(
  int $start,
  int $len,
): ImmVector<Tv>;

$start is 0-based. $len is 1-based. So slice(0,2) would return the elements at key 0 and 1.

The returned ImmVector will always be a subset (but not necessarily a proper subset) of the current ImmVector. If $start is greater than or equal to the length of the current Vector, the returned Vector will contain no elements. If $start + $len is greater than or equal to the length of the current Vector, the returned Vector will contain the elements from $start to the end of the current Vector.

If either $start or $len is negative, an exception is thrown.

Parameters

• int $start - The starting key of the current ImmVector at which to begin the returned ImmVector.
• int $len - The length of the returned ImmVector.

Returns

• ImmVector<Tv> - An ImmVector that is a subset of the current ImmVector starting at $start up to but not including the element $start + $len.

Examples

See Vector::slice for usage examples.