AMDG On 9/20/2010 8:50 AM, dherring@ll.mit.edu 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.).
As a side note, we also must expose both the type of the "which" and the discriminant to member mapping (which may be N:1; see the CORBA IDL spec). So I believe boost::variant would still be hard to use even if the heap issue were resolved.
In Christ, Steven Watanabe