# Module BatMarshal

    module BatMarshal: sig .. end

Marshaling of data structures.

This module provides functions to encode arbitrary data structures as sequences of bytes, which can then be written on a file or sent over a pipe or network connection. The bytes can then be read back later, possibly in another process, and decoded back into a data structure. The format for the byte sequences is compatible across all machines for a given version of Objective Caml.

Warning: marshaling is currently not type-safe. The type of marshaled data is not transmitted along the value of the data, making it impossible to check that the data read back possesses the type expected by the context. In particular, the result type of the `Marshal.from_*` functions is given as `'a`, but this is misleading: the returned Caml value does not possess type `'a` for all `'a`; it has one, unique type which cannot be determined at compile-type. The programmer should explicitly give the expected type of the returned value, using the following syntax:

- `(Marshal.from_channel chan : type)`. Anything can happen at run-time if the object in the file does not belong to the given type.

The representation of marshaled values is not human-readable, and uses bytes that are not printable characters. Therefore, input and output channels used in conjunction with `Marshal.output` and `Marshal.input` must be opened in binary mode, using e.g. `BatPervasives.open_out_bin` or `BatPervasives.open_in_bin`; channels opened in text mode will cause unmarshaling errors on platforms where text channels behave differently than binary channels, e.g. Windows.

This module extends Stdlib's Marshal module, go there for documentation on the rest of the functions and types.
Author(s): Xavier Leroy (base module), David Teller

    val output : 'a BatInnerIO.output -> ?sharing:bool -> ?closures:bool -> 'b -> unit

`output out v` writes the representation of `v` on `chan`.
`sharing` : If `true` (default value), circularities and sharing inside the value `v` are detected and preserved in the sequence of bytes produced. In particular, this guarantees that marshaling always terminates. Sharing between values marshaled by successive calls to `output` is not detected, though. If `false`, sharing is ignored. This results in faster marshaling if `v` contains no shared substructures, but may cause slower marshaling and larger byte representations if `v` actually contains sharing, or even non-termination if `v` contains cycles.
`closures` : If `false` (default value) marshaling fails when it encounters a functional value inside `v`: only ``pure'' data structures, containing neither functions nor objects, can safely be transmitted between different programs. If `true`, functional values will be marshaled as a position in the code of the program. In this case, the output of marshaling can only be read back in processes that run exactly the same program, with exactly the same compiled code. (This is checked at un-marshaling time, using an MD5 digest of the code transmitted along with the code position.)

    val input : BatInnerIO.input -> 'a

`input inp` reads from `inp` the byte representation of a structured value, as produced by one of the `Marshal.to_*` functions, and reconstructs and returns the corresponding value.

    val to_channel : 'a BatInnerIO.output -> 'b -> Marshal.extern_flags list -> unit

Deprecated.Use `BatMarshal.output` instead

    val from_channel : BatInnerIO.input -> 'a

Deprecated.Use `BatMarshal.input` instead