On 09/22/2015 12:52 PM, Ola Fosheim Grøstad wrote:
On Tuesday, 22 September 2015 at 19:38:35 UTC, Ali Çehreli wrote:
C++'s approach is better from the point of view of corretness.
However, it is slower because the object's vtbl pointer must be
stamped several times during construction. (I am not aware of
available compiler optimizations there.)
No dispatch needed if calls it's own functions, so no vtable needed for
the constructor. But neither approach is good for correctness.
Agreed. Only if all potential virtual uses of the object inside the ctor
can be proven to be to the base's type, then yes, setting the vtbl
pointer can be elided.
However, it is not possible in general e.g. if the object is passed to a
function by reference, that function can call any virtual method on it
so the vtbl pointer must have been set upon entry to the constructor, at
every level of the hierarchy.
(OP: The guidelines have 30 committers or something, I somehow doubt
Stroustrup wrote all that...)
I tried to determine the actual author. It was not easy and I still
don't know. :)
Ali
