Re: [boost] Re: shared_ptr comparison

From: Greg Colvin (gcolvin_at_[hidden])
Date: 2001-08-06 13:28:03

From: Daryle Walker <darylew_at_[hidden]>
> on 8/20/01 12:02 AM, Greg Colvin at gcolvin_at_[hidden] wrote:
> 
> [SNIP]
> > And finally, the Core group "broke" auto_ptr in Tokyo, so we also
> > need a core language change to make it work as designed.  If we
> > can't get that change we need to fix the specification to fit
> > reality, or perhaps specify auto_ptr in terms of semantics with
> > no mention of auto_ptr_ref, and tell implementers to just "make
> > it so".
> [TRUNCATE]
> 
> What did the Core group do, and why is it considered a "break"?

I put "broke" in quotes, as what they did was on the edge
between "breaking" and "refusing to fix".  In brief, Bill
Gibbons' rescued auto_ptr at the last moment by coming up
with a very clever implementation to allow the auto_ptr
to have it's bizzare copy semantics by using (some say
abusing) some obscure loopholes in the language.

After struggling for years, Steve Adamczyk failed to find
a way to make the EDG compiler handle line 16 below, and
the committee decided that the language should not support
the loophole that was needed to make it work.

#include <memory>                         //  1
struct Base {                             //  2
   static void sink(auto_ptr<Base>);      //  3
};                                        //  4
struct Derived : Base {                   //  5
   static void sink(auto_ptr<Derived>);   //  6
};                                        //  7
auto_ptr<Derived> source() {              //  8
   auto_ptr<Derived> p(source());         //  9
   auto_ptr<Derived> pp(p);               // 10
   Derived::sink(source());               // 11
   p = pp;                                // 12
   p = source();                          // 13
   auto_ptr<Base> q(source());            // 14
   auto_ptr<Base> qp(p);                  // 15
   Base::sink(source());                  // 16
   q = pp;                                // 17
   q = source();                          // 18
   return p;                              // 19
}