Re: [boost] Interest in an 'either' library?

Subject: Re: [boost] Interest in an 'either' library?
From: David Sankel (camior_at_[hidden])
Date: 2013-06-24 00:26:20

On Sun, Jun 23, 2013 at 5:07 AM, Mathias Gaunard <
mathias.gaunard_at_[hidden]> wrote:

> On 22/06/13 15:11, David Sankel wrote:
>
>  Good question. I think the tradeoffs that were made with Boost.Variant in
>> that case would work just as well here.
>>
>
> Don't you already have an implementation? What does it do?

I do, now that you ask, at https://github.com/camio/Boost.Either. This
reference implementation uses Boost.Variant as a back-end and thus inherits
a lot of its behavior.

Let me try to summarize what precisely happens in the case you were
originally inquiring upon (what happens with exceptions in assignments):

   1. For types where this can happen, the resulting state will still have
   all the invariants of the either type met. That is, it will always refer to
   either a 'left' or a 'right' value.
   2. Because of point one, the use of internal types that have throwing
   assignments may incur an allocation during these operations in order to
   ensure #1 is met.
   3. Ways will be provided to workaround the overhead in #2 for capable
   types.

More details here:
http://www.boost.org/doc/libs/1_49_0/doc/html/variant/design.html#variant.design.never-empty

-- David Sankel