Re: [boost] [utility/value_init] boost::value_initialized<T> direct-initialized?

Subject: Re: [boost] [utility/value_init] boost::value_initialized<T> direct-initialized?
From: Jeffrey Hellrung (jhellrung_at_[hidden])
Date: 2010-03-30 16:50:13

Niels Dekker - address until 2010-10-10 wrote:
> Can anybody please have a look at the following feature request by 
> Edward Diener? https://svn.boost.org/trac/boost/ticket/3472 He proposed 
> to add an explicit constructor, value_initialized(T const&), to 
> boost::value_initialized<T>. This constructor would copy the value of 
> its argument to the object held by value_initialized<T>.
> 
> When such a constructor would be added, an object held by 
> value_initialized<T> might no longer be value-initialized. Instead it 
> might be direct-initialized. Does anybody have any moral (?) objections 
> against the idea that value_initialized<T> might hold a 
> non-value-initialized object?
> 
> Personally I think it would be useful to allow the wrapped object to be 
> direct-initialized. But I do think there's a small risk that the new 
> explicit constructor might cause ambiguities in legacy user code. 
> Therefor I suggested adding an extra "tag" parameter to the new 
> constructor, of a new type, boost::direct_initialized_t:
> 
>   struct direct_initialized_t { };
>   value_initialized(T const&, direct_initialized_t)
> 
> Does anyone else also think that's a good idea? Or does anyone prefer 
> the explicit value_initialized(T const&) constructor originally proposed 
> by Edward?
> 
> See also the thread starting at:
> "Re: [boost] Transfer of Maintenance Rights (utility/value_init)"
> http://lists.boost.org/Archives/boost/2010/03/164125.php
> 
> Kind regards,
> 
>   Niels

Is defining a new template class (e.g., value_or_direct_initialized<T>, 
or whatever) out of the question?  Just a suggestion, and not confident 
it's a good one...

- Jeff