Ivar_filler is a reference to an ivar that allows one to fill the ivar, but not to
read it. This allows the implementation to drop the reference to the ivar once it is
full, which can be useful to avoid holding onto unused memory.
include sig ... endval sexp_of_t : ('a ‑> Sexplib.Sexp.t) ‑> 'a t ‑> Sexplib.Sexp.tinclude Core_kernel.Invariant.S1 with type a t := a tval invariant : 'a Base__.Invariant_intf.inv ‑> 'a t Base__.Invariant_intf.invval create : unit ‑> 'a t * 'a Async_kernel__.Deferred0.tval is_empty : 'a t ‑> boolval fill : 'a t ‑> 'a ‑> unit