Ephemeron

Ah!—so frail are we— So like the brief ephemeron that wheels Its momentary round, we scarce can weep Our own bereavements, ere we haste to share The clay with those we mourn.

Beyond type safety, OCaml has several features that closely interact with the garbage collector. These include weak references, finalisers, ephemerons, and lazy values, whose semantics will have to be preserved with the new GC so as to not break programs that use those features.