[boost] Re: unions

From: David Abrahams (dave_at_[hidden])
Date: 2003-10-08 16:35:14

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

> --- David Abrahams <dave_at_[hidden]> wrote:
>> > I guess the problem is I can't really think of a situation where it makes
>> > any difference if the variant contains the prepended empty_type or
>> > a type from the original list. I'm guessing you can though, so please
>> > help me understand.
>> 
>> Just go back to the original design rationale for variant.  If it
>> really doesn't matter, variant should just prepend empty_type
>> internally and always.  Then we can stop having this discussion ;-)
>
> You have my vote on that.
> I am going to be using variant a lot in my library. 
> I'd really like to get it right.

Just to be clear, I wasn't seriously suggesting that change.  If
that's what you want always, just prepend empty_type yourself; cheap
and easy.  It seems to me that Eric's chosen invariant is a useful
one, and I'm not at all convinced that unconditionally preventing
people from having that invariant is more right than the current
design.

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