iOS uses memory compression but not swap. iOS devices actually have special CPU instructions to speed up compression of up to page size increments specifically to aid in this model [1]

[1] https://github.com/apple-oss-distributions/xnu/blob/bb611c8f...

IIRC from WWDC they said that inactive/suspended apps get their memory compressed to free up memory for the current active/foreground app.

Seems to mesh well with the iOS idea of using a single app at a time and minimizing background processing in apps that you aren't actively using.

In an out of memory situation I think apps just get killed as you suggest.