🚀 go-pugleaf

>>>>> "JM" == Jason Merrill <jason@cygnus.com> writes:

>>>>> Michael McCarty <mikem@eai.com> writes:
 >> How exactly is dynamic_cast<T> supposed to be implemented in the compiler?

 >> It seems to me that the only way to implement this is to attach a type
 >> 'pointer' to every object instantiated, similar to virtual function
 >> pointer tables.

 >> Tell me it ain't so...

 JM> It ain't so.  Dynamic typing is only supported for polymorphic types --
 JM> classes with virtual functions.  The RTTI pointer goes into the vtable in
 JM> all implementations I know about.

What if I use `dynamic_cast' where `static_cast' would be sufficient?  Is the
type /still/ required to be polymorphic?  For example, given this:

 struct B {};
 struct D : B {};
 D* d;

is this expression valid?

 dynamic_cast<B*>(d)

(Why would I write such code?  Well, the types `B' and `D' might have been
parameters to a template in which I did not want to assume the use of
`static_cast' would be proper.)

Michael.


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