Re: [boost] [date_time] bug with time_duration serialization moving from 1.32.0 to 1.33.1

From: Jeff Garland (jeff_at_[hidden])
Date: 2007-01-11 09:46:24

Russell Hind wrote:
> Hi, we've been serializing data to binary archives since serialization 
> was first released.  As such we have collected a lot of data files.
> 
> They are serialized using C++Builder 6 and boost-1.32.0.
> 
> We're now looking to move to VS 2005 and as such, boost-1.33.1 seems a 
> much easier solution than trying to get 1.32.0 to run.
> 
> But I've had trouble de-serializing archives created with BCB6 and 
> 1.32.0 with VS 2005 and 1.33.1.  I've found the problem in time_duration 
> serialization.

I see -- I take it this was the change that fixed serialization of special 
values:  time_serialize.hpp 1.6 to 1.7?

> Its serialization was changed between 1.32.0 and 1.33.1 but no version 
> increment occured.  As such, 1.33.1 can't read archives created with 
> 1.32.0 because of this.
> 
> A version could be added to 1.33.1 now to check for this, but I guess 
> this would then break all archives currently written with 1.33.1.
> 
> For us, we're trying to move to C# so I guess we will mostly be using 
> boost for backwards compatibility for the foreseeable future so our 
> solution is to add a #define to the 1.33.1 header that makes it behave 
> like 1.32.0 did which enables us to load our files.
> 
> But I'm not sure how you would solve this for other users or what to do 
> before 1.34.0.  This situation isn't ideal as can't think of a solution 
> without breaking compatibility at some point.

Well, I think at a minimum there needs to be a warning in the documentation. 
The only other obvious solution would be to provide a macro to allow the 
switchback to the old, broken, behavior.  The other possibility I could see is 
to provide a macro which allows a program that takes the input the old format 
and the output the new format.  This allows for creation of an archive 
conversion program and hence an upgrade path.

> But as a last thought, please can people be careful when modifying 
> serialization functions to keep backwards compatibility.  This has taken 
>   quite a while to track down but that isn't nearly as scary as not 
> being able to move forward to another version of boost without loosing 
> the ability to load in all our customers data.

Thx for the report -- I clearly didn't understand the potential impact of this 
change.  At a minimum there will be doc notes in 1.34.

Jeff