HH\Lib\Keyset\flatten

This API is part of the Hack Standard Library, not HHVM itself.

Returns a new keyset formed by joining the values within the given Traversables into a keyset

namespace HH\Lib\Keyset;

function flatten<Tv as arraykey>(
    Traversable<Traversable<Tv>> $traversables,
): keyset<Tv>;

For a fixed number of Traversables, see Keyset\union().

Parameters