[boost] Re: unions

From: David Abrahams (dave_at_[hidden])
Date: 2003-10-08 20:49:35

"E. Gladyshev" <egladysh_at_[hidden]> writes:

> --- David Abrahams <dave_at_[hidden]> wrote:
> [...]
>
>> > I thought that you have been arguing that it is not
>> > easy to add empty_type especially in generic context?
>> 
>> No, I've been saying that if you add empty_type to types (A,B,C), you
>> lose the valuable invariant that the variant always contains one of
>> (A,B,C).  The invariant becomes that it contains one of
>> (A,B,C,empty_type).  Your code now has to account for that case, and
>> may have to include new cases which fail at runtime.  Consider
>> visitors.
>> 
>
> I agree with that. So what is the conclusion?

That Eric made the change I wanted.

Thanks, Eric!

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com