--- Douglas Gregor <[EMAIL PROTECTED]> wrote: > On Friday 15 November 2002 03:36 pm, Gennaro Prota wrote: > > of inventing a separate concept (say "Addressable") for them. The problem I > > see in your resolution is that AFAIK addressof() is not guaranteed to work > > by the standard. Yes, it has an extremely high probability to do the right > > thing, but not a guarantee. > > You'll have to back that up with some standardese. AFAICT, 5.2.10/10 lets > addressof() work: > "That is, a reference cast reinterpret_cast<T&>(x) has the same effect as > the conversion *reinterpret_cast<T*>(&x) with the builtin & and * operators." > > (And that reinterpret casting T* -> U* -> T* preserves the original value).
Yes, I do know that paragraph. I think it needs some modification if one wants to make clear that the above is allowed. Basically when I read the standard I take a conservative approach, i.e. if there's the slightest doubt that my situation is not what the text guarantees to work I consider myself in an undefined case. Now, let me say that there's an explicit contradiction (as usual in such scenarios where a "special" case is assumed to be specified separately) between 5.2.10/10 and 5.2.10/7, because the latter says that in reinterpret_cast<T*>(&x) you can only cast back the result to the source type, whereas 5.2.10/10 defines the reference-cast in terms of pointer-cast and says it's ok to *dereference* the resulting value. However the real issue is that we have first T -> cv char& -> char & and then char * -> T* The latter is a reinterpret_cast from an rvalue of type char*, so except that I can cast it back to a char* the result is unspecified. The problem exists because the definitions are (correctly IMHO) given in terms of "expressions" (lvalue/rvalue) not of objects, and thus from the perspective of the last cast you "miss" the fact that actually you are dealing with the address of a T: the expression has still type char*, no matter what the type of the object actually is. In short, I agree with you that probably the intent is for it to work. But I think that should be clarified. Genny. __________________________________________________ Do you Yahoo!? Yahoo! Web Hosting - Let the expert host your site http://webhosting.yahoo.com _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
