Re: [Boost-users] [serialization]

From: Daryle Walker (darylew_at_[hidden])
Date: 2005-11-13 06:38:02

On 11/9/05 11:15 PM, "Robert Ramey" <ramey_at_[hidden]> wrote:

> Nigel Rantor wrote:
>> Pragmatic:
>> 
>> Well, how about simply treating anything other than 1 as false? I
>> realise this means that you are implicitly initialising someone elses
>> variable should they serialise and then deserialise but it would seem
>> to preserve the effect that you would witness should you use such a
>> variable without performing that set of operations anyway so it would
>> be an "invisible" side-effect.
>> 
>> Correct:
>> 
>> Initialise all your variables. Shoot all programmers who don't!
>> 
>> And of course, the one true way - tell everyone to initialise their
>> variables or bad things might happen and then be lenient on parsing
>> anyway.
> 
> Actually, my preferred way would be to trap the usage of an unitialized bool
> variable when it is saved.  Its not clear that I can do this.  But a close
> substitute might be to convert the variable to an integer, throw an exception
> if its not equal to 0 or 1 and serialize it otherwise.

The "Correct" method given is the only way.  There's no way to detect
uninitialized variables.  (Anyone who took the effort to offer you a flag
could have initialized the object instead.)  You can't convert it to an
integer, since that also requires reading an uninitialized variable.  Games
with "unsigned char [sizeof(bool)]" won't really work since the bit
pattern(s) for each Boolean state is unspecified.

As I understand it, the serialization layout of a type's components is up to
the author.  That means you can be selective:

    struct my_brokenness
    {
        bool  is_next_one_valid;  // if FALSE, don't set...
        bool  the_real_value;     // ...this member.
        int   other;
    };

    archive &  operator & ( archive &a, my_brokenness &b );
    {
        // the WRONG way
        a & b.is_next_one_valid & b.the_real_value & other;
 
       // the RIGHT way
        a & b.is_next_one_valid;
        if ( b.is_next_one_valid )  a & b.the_real_value;
        a & other;

        return a;
    }

Something like this is required if a member is a "union," right?

-- 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT hotmail DOT com