Re: [boost] boost::nil

From: Douglas Gregor (gregod_at_[hidden])
Date: 2001-06-08 09:40:43

That's worse :(. Anything with "pointer" would be a mistake, IMHO. Maybe 
"null" instead? Any objections to "null"?

        Doug

On Friday 08 June 2001 09:59 am, you wrote:
> Just give it a better name, like null_pointer :)
>
> On Fri, 8 Jun 2001, Chris Little wrote:
> > Doug,
> >
> > Unfortunately adding nil will prevent anyone who is building Macintosh
> > software from using Boost.
> >
> > On a Mac, nil is a preprocessor macro included in the system headers as a
> > legacy of the days when the OS had a Pascal interface.
> >
> > Chris
> >
> > > -----Original Message-----
> > > From: Douglas Gregor [mailto:gregod_at_[hidden]]
> > > Sent: Thursday, June 07, 2001 9:06 PM
> > > To: boost_at_[hidden]
> > > Subject: [boost] boost::nil
> > >
> > >
> > > Hello all,
> > > 	The function library currently under review contains a
> > > type 'nil_t' with an
> > > instance 'nil'. It is a replacement for "0" or "NULL" in any
> > > code. The
> > > implementation is trivial, but it should probably be placed
> > > in its own header
> > > because it's usefulness extends beyond 'function'. The code is just:
> > >
> > > namespace boost {
> > >   struct nil_t
> > >   {
> > >     template<typename T> operator T*() const { return 0; }
> > >     template<typename T, typename U> operator T U::*() const
> > > { return 0; }
> > >   };
> > >
> > >   template<typename T>
> > >   inline bool operator==(const T* p, const nil_t&) { return !p; }
> > >
> > >   template<typename T>
> > >   inline bool operator==(const nil_t&, const T* p) { return !p; }
> > >
> > >   template<typename T>
> > >   inline bool operator!=(const T* p, const nil_t&) { return p; }
> > >
> > >   template<typename T>
> > >   inline bool operator!=(const nil_t&, const T* p) { return p; }
> > >
> > >   namespace {
> > >     nil_t nil;
> > >   }
> > > }
> > >
> > > Advantages of 'nil' over NULL:
> > > 	- NULL is not necessarily portable. Some C++ compilers
> > > pick up bad
> > > definitions of NULL from the system C libraries, making it useless.
> > > 	- The type of NULL is unspecified, so it is impossible
> > > to overload a
> > > function based on it.
> > >
> > > Advantages of 'nil' over 0:
> > > 	- 0 is an integer. It converts to pointer types but
> > > doesn't convey much
> > > information to the user.
> > > 	- the type of 0 is "const int". Overloading a function
> > > to take a null value
> > > based on const int also allows any integer value to be passed
> > > in, and the
> > > error cannot be detected at compile-time.
> > >
> > > 	Doug
>
> ----------------------------------------------------------------------
>  Jeremy Siek                        www: http://www.lsc.nd.edu/~jsiek/
>  Ph.D. Candidate, IU B'ton          email: jsiek_at_[hidden]
>  Summer Manager, AT&T Research      phone: [phone]
> ----------------------------------------------------------------------
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