Re: Implicit cast from derived to base == static_cast
abhay.burli@gmail.com wrote:
AFAIK, implicit cast in C++ has semantics of a static_cast.
And that is completely false, thankfully.
Implicit conversions, explicit conversions and static_cast are all
different things. However, if you can convert implicitly, you can
convert explicitly, and if you can convert explicitly, you can cast
statically.
The same in the other direction is not true, however.
[...]
Thanks for the input. But if implicit cast is indeed same as
dynamic_cast,
I cannot see where anyone has said this. Indeed what we have been
telling you is that each cast is different though some are subsets of
others.
how would an implicit derived to base cast work, on non-
polymorphic classes and where we have a compiler that would allow us
to switch-off RTTI (Ex. MSVC++) ?
The way the language spec says it should.
Question-2:
Can i vindicate my understanding of Question-1 above with the
following code as proof! [...]
12. anA = dynamic_cast<A*>(aB);
If this compiles, your compiler has a bug.
Its MS Visual Studio Team Edition 2005. I tried on comeau and it too
does not complain. I thought comeau was a reliable compiler :-)
It is and because of the potential for a cross cast the line in question
has to be accepted by the implementation until it can prove that the
cross cast is not available (usually this is at execution time but it
could be at link time with a sufficiently intelligent linker.
Looks like there are no simple relationships between implicit, static
and dynamic casts.
There is a perfectly reasonable relationship between implicit casts and
static casts. The former is a subset of the the latter. Dynamic casts
are a completely different breed of cast. In general a dynamic cast can
only be checked at execution time though the implementation is permitted
to do it earlier if that is possible. That actually means that
successful dynamic casts can sometimes be done statically but failure
almost certainly will only be detected at runtime.
{ edits: quoted sig removed. please don't quote extraneous material. -mod }
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