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Module type
Class type
type t
include Ppx_compare_lib.Comparable.S with type t := t
val compare : t -> t -> int
val sexp_of_t : t -> Sexplib0.Sexp.t
include Binable.S with type t := t
include Binable.S_only_functions with type t := t
val bin_size_t : t Size.sizer
val bin_write_t : t Write.writer
val bin_read_t : t Read.reader
val __bin_read_t__ : (int -> t) Read.reader

This function only needs implementation if t exposed to be a polymorphic variant. Despite what the type reads, this does *not* produce a function after reading; instead it takes the constructor tag (int) before reading and reads the rest of the variant t afterwards.

val bin_shape_t : Shape.t
val bin_writer_t : t Type_class.writer
val bin_reader_t : t Type_class.reader
val bin_t : t Type_class.t
val length : t -> int

For performance's concern, we require caller of to_opaque and of_opaque_exn to pass in the buf as the intermediate buffer for bin_prot conversion. These two functions will write bytes into the buffer, but will not resize the buffer. So the caller should prepare big enough buffer for their need.

For of_opaque_exn t, the minimum buffer size should be length t.

For to_opaque the necessary buffer size can be computed using size from Type_class.writer or you can catch the exception Bin_prot.Common.Buffer_short (although the latter is not very reliable because some custom bin_io implementations raise a different exception).

Additional caveat: if the opaque blob is malformed/partial then of_opaque_exn can read past the end of the blob, which can result in:

  • confusing/non-deterministic error messages (referring to the contents of buf rather than the contents of the blob)
  • degraded performance (having to read through the buffer just to fail at the end)
val to_opaque : buf:Common.buf -> 'a -> 'a Type_class.writer -> t
val of_opaque_exn : buf:Common.buf -> t -> 'a Type_class.reader -> 'a