[bind10-dev] suggested team call agenda

[Francis Dupont]

> At Wed, 12 Dec 2012 08:30:57 +0000,
> Francis Dupont <fdupont at isc.org> wrote:
> 
> > > Yeah, in this discussion, we should at least distinguish the direct
> > > use of pointer value as boolean like
> > > 
> > >   Foo* foo;
> > >   if (foo) {
> > >      ...
> > >   }
> > 
> > => IMHO this is bad style because foo is in no way a boolean.
> 
> On reading the language spec again, I realized I overlooked one thing.
> Pointers can be converted to boolean per the standard conversion
> rules:
> 
>   "An rvalue of arithmetic, enumeration, pointer, or pointer to member
>   type can be converted to an rvalue of type bool. A zero value, null
>   pointer value, or null member pointer value is converted to false;
>   any other value is converted to true."
> 
> So, except that it relies on implicit conversion, this is actually
> type safe in C++.  Relying on implicit *something* is itself
> controversial in general, but that equally applies to relying on the
> type conversion operator for shared_ptr.  To this end I now don't see
> a reason for ban this style for bare pointers if we accept it for
> shared_ptr at least in terms of type safety.
> 
> Remaining issue to me is the fact of relying on the implicit
> conversions and consistency with the BIND 9 style
> (http://bind10.isc.org/wiki/BIND9CodingGuidelines "Null Pointer").
> 
> As for the former, I'd generally be careful about relying on implicit
> conversions simply for some seeming convenience.  But this semantics
> for pointers/pointer-like-types is quite common, so I'm personally
> okay with using it in this case.
> 
> As for the latter, I'm basically neutral, but slightly inclined to
> break the consistency, considering the balance between advantages and
> drawbacks.
> 
> ---
> JINMEI, Tatuya

=> I have two comments about this issue which can be summarized by the
same "C++ is not C":

 - in C there is not implicit or explicit conversion to boolean,
  nor in fact a boolean type, so the only correct choice is to
  compare pointers with NULL.

 - in C++ there is no NULL: it is imported from C for compatibility
  but formally pointers should be compared with (or assigned to) 0
  or in last C++ specs nullptr.

Because of the second item now I believe to ban implicit conversion in
this case has no a positive pros vs cons.

Regards

Francis Dupont <fdupont at isc.org>