Re: [Boost-users] Boost Serialization + Forward compatibility [was Re: boost::serialization and PHP websites]

Subject: Re: [Boost-users] Boost Serialization + Forward compatibility [was Re: boost::serialization and PHP websites]
From: Robert Ramey (ramey_at_[hidden])
Date: 2009-06-01 01:58:19

Sohail Somani wrote:
> Steven Watanabe wrote:
>> AMDG
>>
>> Robert Ramey wrote:
>>> Sohail Somani wrote:
>>>
>>>> Just typing out loud: Forward compatibility is the ability to load
>>>> an archive with a version of 4 into an application with a version
>>>> of 3.
>>>>
>>>
>>> To me forward compatability is he ability to create a version 3
>>> archive with a version 4 program.  Hmmm - now that I read that, it
>>> doesn't look right. I guess that should be called "complete"
>>> backward compatibility.  I don't see how it is possible while
>>> writing version 3 progam to know what version 4 is going to save.
>>>
>>
>> It would be possible in special cases.  For example, the
>> version 4 archive could add information that the version
>> 3 program knows to skip somehow.
>
> Right, so one totally naive way the library could do it would be to
> inject a marker after every serialization call. This way, the version
> 3 application could simply search for the marker after every
> serialization call in order to set up the next serialization call.
>
> Basically, I am saying that version 4 of the app writes out:
>
> foo 1 2 3 |END_MARKER| foo 4 5 6 |END_MARKER|
>
> And version 3, which can only read the first two ints, reads foo 1 2
> and then resets the stream pointer (or whatever) to right after
> |END_MARKER|.
>
> If that makes ANY sense, I will be happy.

You might be able to implement that for xml archives by
deriving from xml_iarchive.

Robert Ramey