Durable is designed to help recover from simple errors when using mutable data types that silently fail and can be easily rebuilt or created anew. A clear candidate is Rpc.Connection.t
val create : to_create:(unit ‑> 'a Async.Deferred.Or_error.t) ‑> is_broken:('a ‑> bool) ‑> ?to_rebuild:('a ‑> 'a Async.Deferred.Or_error.t) ‑> unit ‑> 'a tto_create tells the Durable how to build a fresh 'a value.
is_broken tests whether the current 'a value can be used. It should return true when
you want the Durable to attempt to rebuild or recreate the 'a.
to_rebuild Is called on the broken 'a. It should return a "fixed" 'a.
When the function with_ below is called, it uses is_broken to test if the current
Durable value is broken. If not, it calls either to_create or to_rebuild. If
to_rebuild is None (as in the default case), the Durable will try to create a fresh
value with to_create.
create does not create the Durable value. The first call to to_create will be made
on the first use of with_.
val create_or_fail : to_create:(unit ‑> 'a Async.Deferred.Or_error.t) ‑> is_broken:('a ‑> bool) ‑> ?to_rebuild:('a ‑> 'a Async.Deferred.Or_error.t) ‑> unit ‑> 'a t Core.Or_error.t Async.Deferred.tcreate_or_fail immediately calls to_create, returning an error if that first
attempt fails. This function will also return an error if the initial durable value is
broken.
val with_ : 'a t ‑> f:('a ‑> 'b Async.Deferred.Or_error.t) ‑> 'b Async.Deferred.Or_error.twith_ applies the given function to the Durable value if is_broken returns
false. If is_broken return true, it first calls to_create or to_rebuild. This
function will return an error if either to_create or to_rebuild returns an error,
or if the rebuilt or recreated durable value is broken. is_broken is checked
immediately before calling f.
We will only make one attempt to rebuild a broken value. If a call to to_rebuild
returns Error _, we will drop the previously built value. The next call to with_
will call to_create.
with_ will raise if f raises.