[ forwarded to C++ committee.  -sdc ]

3.8 [basic.life] and 12.4 discuss explicit management of object lifetime.
It seems clear that most object lifetime issues apply to sub-objects (array
elements, and data members) as well.  The standard supports

     struct X { T t } x;
     T* pt = &x.t;
     pt->~T();
     new(pt) T;

and this kind of behavior is useful  in allocators.

However the standard does not seem to prohibit the same operations on base
sub-objects.

   struct D: B{ ... } d;
   B* pb = &d;
   pb->~B();
   new(pb) B;

however if B and/or D have virtual member functions or virtual bases, it is
unlikely that this code will result in a well-formed D object in current
implementations (note that the various lines may be in different functions).

I suggest that 12.4 be modified so that explicit destruction of base-class
sub-objects be made illegal, or legal only under some restrictive
conditions.




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