🚀 go-pugleaf

In article <CLINE.90Aug27124642@cheetah.ece.clarkson.edu> cline@sun.soe.clarkson.edu (Marshall Cline) writes:
| In article <48168@brunix.UUCP> sdm@cs.brown.edu (Scott Meyers) writes:
| > Does E&S prohibit explicit casts from pointers to virtual base classes to
| > pointers to derived classes?
| 
| Yes, these casts, even though explicit, are illegal.  The July issue of
| The C++ Report contains a C++ Puzzle solution showing why.  Basically
| there is no way of knowing at compile time how to perform the cast.  The
| cover article in the same issue shows a portable method of faking the
| cast.  The method requires maintaining run-time type information.

Do you have a reference for where in E&S they are declared illegal?  As I
said, I found such a prohibition only in the commentary.

Unfortunately, I don't have access to the C++ Report, but the commentary of
E&S outlines an implementation for virtual base classes that makes it
impossible to do downward casts such as I described, and I suspect this is
the implementation discussed in the C++ Report.  As the discussion in E&S
implies, there are alternative implementations for virtual bases that allow
for well-defined downward casts, but they require more memory per object.

Scott