Path: utzoo!mnetor!uunet!husc6!mit-eddie!uw-beaver!tikal!hplsla!jima
From: jima@hplsla.HP.COM (              Jim Adcock)
Newsgroups: comp.lang.c++
Subject: Re: const, reference "this" revisited ???
Message-ID: <6590015@hplsla.HP.COM>
Date: 1 Feb 88 22:29:43 GMT
References: <6590014@hplsla.HP.COM>
Organization: HP Lake Stevens, WA
Lines: 21

In response to the vast amount of excitment this note has generated,
let me say I am tending to rethink this subject.  Per conversations
with MTD and Glen Purdy here, it should be possible to use a variety
of register passing schemes for "this' and the "vtable" pointer that
will avoid most inefficiencies, even if the called routine is unable
to declare (this*) const or not.

Ideally, this, and this->vtable are passed to the called (virtual)
routine using a register passing scheme.  The called routine knows
whether vtable gets poisoned by an assignment to (this*) and can
update vtable accordingly before it exits.

PS:

If you are a c++ compiler writer, I sure would lobby for the idea
of passing "this" and "this->vtable" using a register passing scheme.
This would not invalidate existing C libraries using a stack passing 
scheme for "normal" variables, since C++ "this" and "this->vtable" 
are NOT "normal" variables, nor do they have an equivalent in normal 
C code.  I guess this "this" register passing scheme could even be 
faked-up in cfront if anyone were so motivated.