Re: Covariant returns?

[Chris Heath <cheath at umich dot edu>]

> I'm wondering if covariant returns are going to be implemented anytime
> soon... I looked on the known bugs page, but I didn't see anything
> about it.
> 
> [code snipped]
> 
> The result:
> x.cpp:7: sorry, not implemented: adjusting pointers for covariant returns


Worse, in the multiple inheritance case, the compiler doesn't produce any
error message, but produces incorrect code. Here's an example:
 
 
#include <stdio.h>
 
struct A {
  virtual A* This() {return this;}
};
 
struct B {
  virtual B* This() {return this;}
};
 
struct C : A, B {
  virtual C* This() {return this;}
};
 
main () {
  C cl;
  C* c=&cl;
  B* b=&cl;
  A* a=&cl;
  printf("%p %p %p\n", c, b, a);
  printf("%p %p %p\n", c->This(), b->This(), a->This());
}
 
 
This compiles without errors with gcc 2.95.2, but its output is (on my
SPARC)
 
effff9b0 effff9b4 effff9b0
effff9b0 effff9b0 effff9b0
 
In other words, b->This() is returning a pointer to an object that is not
of type B.
 
 
Chris