[boost] Re: In-place construction for variant

From: David Abrahams (dave_at_[hidden])
Date: 2003-10-27 12:18:29

Eric Friedman <ebf_at_[hidden]> writes:

>>    v.construct<T>(args)
>> is calling a nothrow constructor, then the "destroy, then create"
>> ordering can still preserve the strong guarantee, it seems.
>
> Variant provides the basic guarantee for assignment lhs = rhs by
> copying the content of lhs onto the heap before its destruction. Then
> the content of rhs is copied to the storage of lhs. In the event of
> success, the backup is destroyed; in the event of an exception, the
> lhs variant stores a pointer to the backup and "redirects" all
> visitation requests accordingly.

What a surprise.  Why would you want to pay for the copy back to the
stack once you've paid for heap allocation?  I guess if you're worried
about sucking up heap memory it might be important.  If you're worried
about speed it could be bad.  Hmm, sounds like a policy :(.

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