Re: [boost] [config] Macro for null pointer

Subject: Re: [boost] [config] Macro for null pointer
From: Nathan Crookston (nathan.crookston_at_[hidden])
Date: 2012-12-06 21:34:43

Andrey Semashev wrote:

> On Thu, Dec 6, 2012 at 7:42 AM, Jeffrey Lee Hellrung, Jr. wrote:
> >
> > Or, as Nathan suggested, drop trying to emulate the literal nullptr
> keyword
> > and just define and use boost::nullptr_. That's probably the best option.
> > Slightly uglier, but no macros and no name collisions.
>
> Nathan's code sample has an error, it always uses
> boost::detail::nullptr_t to define nullptr_. After correcting this I'm
> not sure that the following:
>
> namespace boost {
>
> typedef std::nullptr_t nullptr_t;
> const nullptr_t nullptr_ = {};
>
> }
>
> is valid and supposed to work. If I'm not mistaken, we know almost
> nothing about std::nullptr_t. In particular, we don't know if it's
> default constructible and if it is, will it be equivalent to nullptr.
>
 The particular initialization of the previous may not be legal, but from
the standard it appears that contructing std::nullptr_t should work.  This
post [1] seems to agree with my reading (and it has references).

> Also, boost::nullptr is supposed to help writing C++11-style code even
> for C++03 compilers. With a different keyword that doesn't hold
> anymore, a migration path is needed. I'm not sure it's worth the
> effort in this case.

True.  It would be nice if there was *something* which was implicitly
convertible to a null shared_ptr<T> (regardless of T) -- that's the biggest
place I miss nullptr in my current code.  Construction from boost::none is
a really nice usability feature of boost::optional.

Thanks,
Nate

[1] <
http://stackoverflow.com/questions/9953068/is-nullptr-t-a-default-constructible-type
>