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From: ttwang@polyslo.CalPoly.EDU (Thomas Wang)
Newsgroups: comp.lang.c++
Subject: Re: multiple destructors
Message-ID: <1989Oct22.220719.29822@polyslo.CalPoly.EDU>
Date: 22 Oct 89 22:07:19 GMT
References: <1989Sep30.190719.3340@polyslo.CalPoly.EDU> <6590273@hplsla.HP.COM> <1989Oct21.182759.13138@paris.ics.uci.edu> <10042@alice.UUCP>
Reply-To: ttwang@polyslo.CalPoly.EDU (Thomas Wang)
Distribution: usa
Organization: Cal Poly State University -- San Luis Obispo
Lines: 37

bs@alice.UUCP (Bjarne Stroustrup) writes:

>Ron Guilmette points out that by being clever you can deduce the storage
>clas of an object from its address by knowing how your machine lays out
>a program in memory. This is not only non-portable, but also unreliable
>in the presense of a co-routine or lightweight process package because
>these tend to have stacks in areas that to the simple single-thread layout
>looks like free store.

This is a good point.  It seems there is no portable way in C++ to tell if
an object is automatic, heap, or static.

A related issue is the ability of C++ to support copying garbage collector.
To directly support garbage collected objects in C++ will introduce overhead
across the board.  But it is possible to make C++ friendly toward
copying garbage collector so that a 'class' implementation is possible.

Two problems are 'this' pointers, and destructors.

'this' pointers are a major problem.  There should be way to redefine 'this'
to another data type, prodived the data type has '->' operator to reach the
data members.

A 'handle' on the stack can be maintained to point to the right place.  A
physical pointer on the stack is impossible to maintain.

Destructors are a minor problem.  There should be an easy way to tell if
an object contains any destructors or not.  Currently this problem can be
solved by maintaining a virtual boolean function  has_destructor(), but it's
a tedious process.


 -Thomas Wang ("This is a fantastic comedy that Ataru and his wife Lum, an
                invader from space, cause excitement involving their neighbors."
                  - from a badly translated Urusei Yatsura poster)

                                                     ttwang@polyslo.calpoly.edu