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From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2007-01-25 09:46:29

I am currently writing an object container similar to boost.any but with
an allocator template parameter. That allocator is of a custom type that
allows efficient stack allocation like boost.variant.

While looking at variant's documentation, I became aware of the problem
with operator= and the never-empty guarantee.

However, I think none of the solutions is really satisfying, especially
in my case where the allocator is generic and provided by the user and
where the types that are to be put in the container aren't known until
Lots of versions would need to be made, indicating whether one or
another option is nothrow for the object or the allocator, providing
fallback allocators etc.

Do you think it is reasonable to simply require a nothrow move
constructor for the types which are to be put into my container?
I cannot think of a case where move constructors would really want to
throw, and swap functions which are similar are usually no-throw.

There is also the 'false hopes' solution, which is said to not be
allowed by the standard.
But realistically, that solution shouldn't cause any problem, since I
always see moving as a simple bitwise copy ; unless the object
references itself, which would be solved by moving it back anyway.

I welcome any critics, ideas and advices about moving, exceptions, and
bitwise copy.

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