package ppx_bin_prot
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Dune Dependency
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sha256=94486e7d6357f12f8aa358196783822c500b3b2fe04c597ea86c1c42bc5c3b61
README.md.html
ppx_bin_prot
Generation of binary serialization and deserialization functions from type definitions. There's more information about:
The bin-prot format
bin-prot-shape, which is useful for checking compatibility of the
bin_prot
representations of different types.
A note about signatures
In signatures, ppx_bin_prot
tries to generate an include of a named interface, instead of a list of value bindings. That is:
type 'a t [@@deriving bin_io]
will generate:
include Binable.S1 with type 'a t := 'a t
instead of:
val bin_t : 'a Bin_prot.Type_class.t ‑> 'a t Bin_prot.Type_class.t
val bin_read_t : 'a Bin_prot.Read.reader ‑> 'a t Bin_prot.Read.reader
val __bin_read_t__ : 'a Bin_prot.Read.reader ‑> (int ‑> 'a t) Bin_prot.Read.reader
val bin_reader_t : 'a Bin_prot.Type_class.reader ‑> 'a t Bin_prot.Type_class.reader
val bin_size_t : 'a Bin_prot.Size.sizer ‑> 'a t Bin_prot.Size.sizer
val bin_write_t : 'a Bin_prot.Write.writer ‑> 'a t Bin_prot.Write.writer
val bin_writer_t : 'a Bin_prot.Type_class.writer ‑> 'a t Bin_prot.Type_class.writer
val bin_shape_t : Bin_prot.Shape.t ‑> Bin_prot.Shape.t
There are however a number of limitations:
the type has to be named t
the type can only have up to 3 parameters
there shouldn't be any constraint on the type parameters
If these aren't met, then ppx_bin_prot
will simply generate a list of value bindings.
Expression extensions
Several new expression forms are supported to derive the individual values defined by ppx_bin_prot
. Each of the following extensions can be used, with arbitrary type expressions in place of t
, to produce values of the corresponding types on the right:
[%bin_shape: t] : Bin_prot.Shape.t
[%bin_digest: t] : string
[%bin_size: t] : t Bin_prot.Size.sizer
[%bin_write: t] : t Bin_prot.Write.writer
[%bin_read: t] : t Bin_prot.Read.reader
[%bin_writer: t] : t Bin_prot.Type_class.writer
[%bin_reader: t] : t Bin_prot.Type_class.reader
[%bin_type_class: t] : t Bin_prot.Type_class.t
Weird looking type errors
In some cases, a type can meet all the conditions listed above, in which case the rewriting will apply, but lead to a type error. This happens when the type t
is an alias to a type which does have constraints on the parameters, for instance:
type 'a s constraint 'a = [> `read ]
val bin_s : ([> `read ] as 'a) Type_class.t0 -> 'a s Type_class.t0
val bin_read_s : ([> `read ] as 'a) Read.reader -> 'a s Read.reader
val bin_reader_s : ([> `read ] as 'a) Type_class.reader0 -> 'a s Type_class.reader0
val bin_size_s : ([> `read ] as 'a) Size.sizer -> 'a s Size.sizer
val bin_write_s : ([> `read ] as 'a) Write.writer -> 'a s Write.writer
val bin_writer_s : ([> `read ] as 'a) Type_class.writer0 -> 'a s Type_class.writer0
val bin_shape_s : Shape.t -> Shape.t
type 'a t = 'a s [@@deriving_inline bin_io]
include Binable.S1 with type 'a t := 'a t
[@@@end]
will give an error looking like:
Error: In this `with' constraint, the new definition of t
does not match its original definition in the constrained signature:
Type declarations do not match:
type 'a t = 'a t constraint 'a = [> `read ]
is not included in
type 'a t
File "binable.ml", line 34, characters 2-11: Expected declaration
Their constraints differ.
To workaround that error, simply copy the constraint on the type which has the [@@deriving]
annotation. This will force generating a list of value bindings.