"Steven Watanabe" <watanabesj@gmail.com> wrote in message news:47DFF458.7010409@providere-consulting.com... [...]
Which compilers? IMO, you shouldn't make the code even more obscure until it's known for certain to be a problem.
Well 0 is considered to be a null pointer, not a pointer to 0x0000. This can potentially be replaced by "nullptr" in the next revision, which shouldn't be assumed to be a pointer to 0x0000. Having a non-null constant removes this nullness ambiguity. I see there is a BOOST_PYTHON_OFFSETOF macro that exists and which uses this technique. It is unfortunate offsetof() doesn't take a real pointer-to-member address.
This address dissosiates the pointer from an undefined behavior and is aligned for all types.
5.5/4: "If the dynamic type of the object does not contain the member to which the pointer refers, the behavior is undefined."
"operator ->" can be used in an address constant expression without being considered to be a dereference because of "operator &". 5.19/4: An address constant expression is a pointer to an lvalue designating an object of static storage duration, a string literal (_lex.string_), or a function. The pointer shall be created explicitly, using the unary & operator, or implicitly using a non-type template parameter of pointer type, or using an expression of array (_conv.array_) or function (_conv.func_) type. The subscripting operator [] and the class member access . and -> operators, the & and * unary operators, and pointer casts (except dynamic_casts, _expr.dynamic.cast_) can be used in the creation of an address constant expression, but the value of an object shall not be accessed by the use of these operators. [...] -Phil