Re: [boost] Re: unions

From: E. Gladyshev (egladysh_at_[hidden])
Date: 2003-10-08 20:00:48

--- 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?

Eugene

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