RE: [Boost-Users] std::swap() vs boost::swap()

From: scleary_at_[hidden]
Date: 2002-09-26 11:52:08

> From: Galante Michele [mailto:M.Galante_at_[hidden]]
> 
> > Argument-dependent lookup will ensure that any 'swap' functions in the 
> > namespaces used by 'T' will be included in the set of known swap
functions,
> > along with std::swap. Overloading and partial ordering of function
templates
> > will then take over to ensure that the appropriate swap(a, b) will be
called 
> > (even if it is boost::swap).
> 
> I did not know this. I suppose this is the "Koenig lookup" that Steve
> mentions in his reply.
> I've tried this and it works with GCC 3.1 but unfortunately 
> not with BCC 5.6
> (so I think it is a Borland bug).

Yes "Koenig lookup" is "argument-dependent lookup", and sadly several
compilers still do not implement it.

There's a workaround for the lack of Borland's support:
  using std::swap; // This should have been in my example to begin with...
  using boost::swap;
  swap(x, y);
Which works on GCC 3.1.1 and BCC 5.6, and I would imagine any other compiler
as well.

The downside is that you have to list in your "generic" function all the
namespaces that it can be used with -- which then makes it not-very-generic
on compilers without Koenig lookup.  But it's better than nothing...

        -Steve