Re: Virtual function call from constructor

From:

Eric Sosman <esosman@acm-dot-org.invalid>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 24 Jun 2007 17:35:55 -0400

Message-ID:

<j6KdnZCfVvlWfuPbnZ2dnUVZ_segnZ2d@comcast.com>

Mike Schilling wrote:

"Eric Sosman" <esosman@acm-dot-org.invalid> wrote in message
news:dp-dnSoXCdbi6OPbnZ2dnUVZ_hadnZ2d@comcast.com...

I *did* use the word "bloat," and it still seems justifiable.
The implementation you describe (if I've understood you correctly)
requires each instance to carry a pointer per inheritance level;
that's certainly larger than the one bit per level I described as
a hypothetical implementation, and that in turn is larger than
no per-instance "construction status" at all.

Not at all. It requires each instance to hold one pointer, period. The
*value* of this pointer is changed during construction.

Aha! So if you've got a class that's N levels deep in the
inheritance hierarchy, you've got N+1 versions of the vtable,
each corresponding to a different amount of progress through
the constructor chain. Is that it?

Hmmm... If that's the way it works, then defining an Nth
level class really defines N+1 distinct classes, in the sense
that a class is the set of its behaviors. If applied to an
object in the midst of construction, which of those N+1 classes
should getClass() return? And how should instanceof behave?

--
Eric Sosman
esosman@acm-dot-org.invalid