From: Robert Klemme <shortcutter@...>
Date: 2008-05-23T18:40:01+09:00
Subject: Re: customized serialization unreliable????

On 23.05.2008 10:33, Andrew Mitchell wrote:
>>    def marshal_dump()
>>       return [@version,@data]
>>    end
> 
> If there are actually classes built on instance methods marshal_dump and 
> marshal_load, then Marshal would be completely ignoring those methods. 

I don't think so, at least not in 1.8.6:

robert@fussel /cygdrive/c/Temp
$ irb
irb(main):001:0> class F
irb(main):002:1> def marshal_dump
irb(main):003:2> puts "dump"
irb(main):004:2> "123"
irb(main):005:2> end
irb(main):006:1> def marshal_load(x)
irb(main):007:2> puts "load #{x}"
irb(main):008:2> end
irb(main):009:1> end
=> nil
irb(main):010:0> Marshal.load(Marshal.dump(F.new))
dump
load 123
=> #<F:0x7ff7be4c>
irb(main):011:0>

> Assuming you meant "_dump" which is the instance method to overload for 
> customized serialization, and either "self._load" or klassname._load 
> which is the class method for the same, then this would be happening:

I believe this is yet another mechanism to control custom marshalling.

> Array.to_s will be called in Marshal.dump because it expects a string.

I don't think so.  The mechanism is different.  It would be too fragile 
to depend on #to_s to return something that can be used to deserialize.

> For example, with the YYY class:
> @version = 1
> @data = ["e", "i"]
> _dump returns [1, ["e", "i"]]
> The Marshaling process will form "1ei"
> 
> Your Loading process with "1ei" will give
> @version = 1
> @data = "e" # instead of ["e", "i"]
> 
> 
> If for whatever reason you are Marshaling the results of your 
> marshal_dump methods -- Marshal.dump(my_yyy.marshal_dump) --, then you 
> have neglected to properly handle object graph cycles, and shared 
> references.

Correct.  See my other posting for a nice example. :-)

All in all I believe, if one wants to exclude some fields from 
serialization (like with "transient" in Java) the best way is to 
implement #marshal_dump to just return an array of the fields that need 
to be serialized and deserialized and implement #marshal_load(ar) 
accordingly.  That way Marshal can properly handle loops in object 
graphs etc.

Kind regards

	robert