Bin_prot.Blob
'a Blob.t
is type-equivalent to 'a
, but has different bin-prot serializers that prefix the representation with the size of 'a
.
To understand where this is useful, imagine we have an event type where many applications look at some parts of an event, but not all applications need to deal with all parts of an event. We might define:
type 'a event =
{ time : Time.t
; source : string
; details : 'a
} [@@deriving bin_io]
Applications that need to understand all the details of an event could use:
type concrete_event = Details.t Blob.t event [@@deriving bin_io]
An application that filters events to downsteam consumers based on just source
or time
(but doesn't need to parse details
) may use:
type opaque_event = Blob.Opaque.Bigstring.t event [@@deriving bin_io]
This has two advantages:
details
is avoidedDetails.t
type, so it's robust to changes in Details.t
An application that's happy to throw away details
may use:
type ignored_event = Blob.Ignored.t event [@@deriving bin_read]
Whereas opaque_event
s roundtrip, ignored_event
s actually drop the bytes representing details
when deserializing, and therefore do not roundtrip.
include Ppx_compare_lib.Comparable.S1 with type 'a t := 'a t
val sexp_of_t : ('a -> Sexplib0.Sexp.t) -> 'a t -> Sexplib0.Sexp.t
include Binable.S1 with type 'a t := 'a id
val bin_size_t : ('a, 'a id) Size.sizer1
val bin_write_t : ('a, 'a id) Write.writer1
val bin_read_t : ('a, 'a id) Read.reader1
val __bin_read_t__ : ('a, int -> 'a id) Read.reader1
val bin_writer_t : ('a, 'a id) Type_class.S1.writer
val bin_reader_t : ('a, 'a id) Type_class.S1.reader
val bin_t : ('a, 'a id) Type_class.S1.t
module Opaque : sig ... end
An Opaque.Bigstring.t
or Opaque.String.t
is an arbitrary piece of bin-prot. The bin-prot (de-)serializers simply read/write the data, prefixed with its size.
module Ignored : sig ... end
An Ignored.t
is an unusable value with special bin-prot converters. The reader reads the size and drops that much data from the buffer. Writing is not supported, however the size of t
is kept, so bin_size_t
is available.