marshalling objects

marshalling objects

[Pietro Abate]

Hi all,

It's not clear to me if it is possible or not to marshall objects ? From
my tests it is not the case (output_value: abstract value (outside
heap).). Am I missing something ? What is common practice to send
objects across the wire ?

thanks,
p

--------- ex.ml

class node = object val d = 1 end ;;

let l =
    try
        let a = (new node) in
        let s = (Marshal.to_string a [])
        in print_endline "Success"; (Marshal.from_string s 0 : node)
    with Invalid_argument s -> print_endline ("Failed "^s) ; (new node)
;;

let l =
    try
        let a = (new node) in
        let s = (Marshal.to_string a [Marshal.Closures])
        in print_endline "Success"; (Marshal.from_string s 0 : node)
    with Invalid_argument s -> print_endline ("Failed "^s) ; (new node)
;;

let l =
    try
        let a = (new node) in
        let s = (Marshal.to_string a [Marshal.No_sharing])
        in print_endline "Success"; (Marshal.from_string s 0 : node)
    with Invalid_argument s -> print_endline ("Failed "^s) ; (new node)
;;

let l =
    try
        let a = (new node) in
        let s = (Marshal.to_string a [Marshal.No_sharing;Marshal.Closures])
        in print_endline "Success"; (Marshal.from_string s 0 : node)
    with Invalid_argument s -> print_endline ("Failed "^s) ; (new node)
;;


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Re: [Caml-list] marshalling objects

[Jacques Garrigue]

From: Pietro Abate <Pietro.Abate@anu.edu.au>

> It's not clear to me if it is possible or not to marshall objects ? From
> my tests it is not the case (output_value: abstract value (outside
> heap).). Am I missing something ? What is common practice to send
> objects across the wire ?

It is possible, but there was a bug in 3.08.
In 3.09, you can marshal an object with
   Marshal.to_string obj [Marshal.Closures]
Note that this means that the method table is really sent, as an array
of closures, which is possibly very innefficient, and also means that
the program on the other side must be the same one.

Jacques Garrigue

Re: [Caml-list] marshalling objects

[sejourne_kevin]

Jacques Garrigue a écrit :
> Note that this means that the method table is really sent, as an array
> of closures, which is possibly very innefficient, and also means that
> the program on the other side must be the same one.

Exactly the same one or just all classes ?
I think this could be in the manual of module Marshal.


Kévin.

	

	
		
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Re: [Caml-list] marshalling objects

[Jacques Garrigue]

From: sejourne_kevin <sejourne_kevin@yahoo.fr>
> Jacques Garrigue a écrit :
> > Note that this means that the method table is really sent, as an array
> > of closures, which is possibly very innefficient, and also means that
> > the program on the other side must be the same one.
> 
> Exactly the same one or just all classes ?
> I think this could be in the manual of module Marshal.

Actually it's just a consequence of the internal representation of
classes, which is described in the C interface section.
That is, each object contains an array with all its methods, which are
function closures.
This is the reason you need the flag for closures.
And the condition with closures is quite explicit: this must be
exactly the same program. I also expect that, for native code, it must
be the same architecture.

Jacques Garrigue

Re: [Caml-list] marshalling objects

[Richard Jones]

On Fri, Apr 25, 2008 at 04:42:02PM -0400, Jacques Le Normand wrote:
> if I marshal an object of class c and I write the result in a file foo.txt
> and, later on, I add methods to c, can I read the object in foo.txt and call
> the new methods on the object?

No.  What are you trying to accomplish?

Rich.

-- 
Richard Jones
Red Hat

Re: [Caml-list] marshalling objects

[Basile STARYNKEVITCH]

Jacques Le Normand wrote:
> hello caml list,
> if I marshal an object of class c and I write the result in a file 
> foo.txt and, later on, I add methods to c, can I read the object in 
> foo.txt and call the new methods on the object?

First, a *.txt extension for a binary file (written thru Marshal.* 
functions) is very confusing.

Second, marshalling of any closures (including methods shared by 
objects) can only be unmarshalled by the exact same binary. So if you 
add/change code, it should not work.


-- 
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