TakeWhile

:::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 Vector containing the values of the current Vector up to but not including the first value that produces false when passed to the specified callback

public function takeWhile(
  (function(Tv): bool) $callback,
): Vector<Tv>;

That is, takes the continuous prefix of values in the current Vector for which the specified callback returns true.

The returned Vector will always be a subset (but not necessarily a proper subset) of the current Vector.

Parameters

• (function(Tv): bool) $callback

Returns

• Vector<Tv> - A Vector that is a subset of the current Vector up until the callback returns false.

Examples

This example shows how takeWhile can be used to create a new Vector by taking elements from the beginning of an existing Vector:

$v = Vector {0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144};

// Include values until we reach one over 10
$v2 = $v->takeWhile($x ==> $x <= 10);
\var_dump($v2);