SOURCE Jason Hise wrote:
>  Martin Wille wrote:
>  
>  
> >Jason Hise wrote:
[...]
> >I also object to this idea in general. It doesn't buy us much, it breaks 
> >existing code, it may cause ODR violations, and it also violates the C++ 
> >Standard.
> >
>  
>  What existing code will it break?  I would imagine it would only break 
>  code that deserves to be broken in the first place (like int i = NULL).

Eric already provided an example for code breaking with your definition 
of NULL.

There's nothing wrong with int i = NULL. It's certainly not good style, 
but that doesn't make it deserve to be broken.


>  Also, how would this cause ODR violations?  I was under the impression 
>  that the one definition rule required all definitions in different 
>  translation units to be identical, not that it required that a 
>  definition only be provided in one translation unit.

a.hpp:
#include "boost/null.hpp"

b.hpp:
#include <cstddef> 

c.hpp:
/* e.g. template code that uses NULL */


x.cpp:

#include "b.hpp"
#include "a.hpp"
#include "c.hpp"

/* use stuff from c.hpp */


y.hpp:

#include "b.hpp"
#include "c.hpp"

/* use stuff from c.hpp */


x and y will instantiate different code due to the different #include order.



   And even if
>  somehow more than one instance of null ended up being used, how would 
>  this actually end up causing a problem?

It's undefined behaviour.


                                         Would your problem with this
>  code vanish if I removed the NULL definition on the last two lines?

Yes.


>  Would it reappear if I moved the null class into the global namespace 
>  (essentially making lowercase null a keyword)?

Adding stuff to the global namespace bears its own set of problems.
You would definitely break a lot of code that defines its own null 
constants. It's certainly less of a problem than re#defining NULL would be.


Regards,
m
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