Re: [boost] [type-traits] aligned_storage in unions

Subject: Re: [boost] [type-traits] aligned_storage in unions
From: dherring_at_[hidden]
Date: 2010-09-20 14:16:01

On Mon, 20 Sep 2010, Steven Watanabe wrote:
> On 9/20/2010 8:50 AM, dherring_at_[hidden] wrote:
>> See
>> http://www.boost.org/doc/libs/1_44_0/doc/html/variant/design.html
>>
>> In particular, "Temporary Heap Backup" and "Future Direction".
>>
>> We have some specialized requirements.  We couldn't even use
>> boost::shared_ptr until it added both the custom allocator and
>> deleter. The "never-empty guarantee" conflicts with our needs and is
>> not a concern at this time.
>
> You can effectively bypass the never-empty guarantee by adding
> boost::blank to the variant types.  This will cause the variant to
> set itself to boost::blank on an exception instead of using heap
> backup.  (This will actually work if has_nothrow_constructor is
> true for /any/ of the variant types, but boost::blank is the preferred
> backup if it's present.).

Thanks for the info; I hadn't noticed that feature.

- Daniel