[boost] Re: unions

From: David Abrahams (dave_at_[hidden])
Date: 2003-10-08 14:15:41

"E. Gladyshev" <egladysh_at_[hidden]> writes:

> --- Daniel Wallin <dalwan01_at_[hidden]> wrote:
> [...]
>
>> I don't yet buy that this is a problem for generic programming;
>> 
>> If variant is part of the program interface, the type shouldn't be changed
>> anyway, so "wanting the benefit of the optimization" becomes the users
>> problem.
>> 
>> If the variant is part of the implementation, where the type sequence
>> is part of the interface, the invariant type is just an implementation
>> detail, or part of the program documentation.
>
> typedef variant< int, my_type > v1;
> typedef variant< my_type, int > v2;
>
> I think that we should just realize that 
> in the current variant, v1 and v2 have 
> a vastly different behaviour.

Really?  What are the differences?

> It just goes against any conventional 
> wisdom and intuition. People, please...
>
> I don't think that the *weak* exception 
> safety (the way it is implement now) 

What is "weak" exception safety?

> is worth it.

IIUC the exception guarantees are the same whether or not the
optimization takes effect.

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