RE: RE: [boost] Does anyone have an is_virtual_base_and_derived ?

From: SRobb_at_[hidden]
Date: 2004-07-08 12:04:15

> > I wrote that very thing a year or so ago for the purpose of 
> testing if a
> > base pointer type can be statically downcast to a derived type.
> 
> My problem exactly !

  I should warn you that this isn't quite enough information to test for
static downcastability in all cases.  Take the following example:

struct b1 {};
struct b2 : b1 {};
struct b3 : virtual b2 {};

  Here, b1 is not a virtual base of b3, but a downcast from b1* to b3* is
still impossible.  I don't believe there is any way to test for this case
without compiler assistance.

  Testing for a virtual base happened to be good enough for us though, so we
went with it; it may well be enough for your needs too.