module BatMarshal:Marshaling of data structures.sig..end
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.Marshal.output and
Marshal.input must be opened in binary mode, using e.g.
ExtPervasives.Pervasives.open_out_bin or
ExtPervasives.Pervasives.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 -> unitoutput 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 -> 'ainput 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
val from_channel : BatInnerIO.input -> 'a