[boost] Re: basic guarantees in variant

From: David Abrahams (dave_at_[hidden])
Date: 2003-10-08 21:03:43

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

> --- David Abrahams <dave_at_[hidden]> wrote:
> [...]
>> variant<std::vector<int>, std::string> v("hello");
>> v = std::vector<int>(3);
>> 
>> First you destroy the contained string, then you try to construct the
>> vector and it throws.  The invariant says you have to contain either
>> a vector or a string, but you can't get the string back; it's likely
>> to throw on construction too.
>> 
>> The only way to maintain the basic guarantee in this case, with this
>> invariant, is to construct the vector, somewhere else, before
>> destroying the string... which means on the heap or in duplicate space
>> in the variant itself.
>
> Could it be done on the stack and not on heap or duplicate space?
> I think that I can outline a solution about how to do it
> w/o heap or duplicate space.

You are a genius.  Please elaborate.

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