Float.infinity. This compiles and works.
In all probability,
HUGE_VALF was a legacy value in any case.
Still, it’s a bit of a surprise that these numeric constant names are not seen by Swift. I did try importing
<stdlib.h> in the bridging header but it didn’t help.
But please see now Martin R’s answer. Since the time when I posted my answer, Apple has stated their preferred answer explicitly: use
.greatestFiniteMagnitude. It is almost the same thing as
.infinity but not quite!