Re: [boost] Re: Optimising assignment using std::swap

From: Stephen Silver (boost_at_[hidden])
Date: 2001-01-24 16:41:15

Darin Adler wrote:

> on 1/23/01 3:27 PM, Stephen Silver at boost_at_[hidden] wrote:
>
> > Daryle Walker wrote:
> > 
> >> Since we can't put specializations of template functions, like "swap",
> >> in the "std" namespace,
> > 
> > But we can.  17.4.3.1 / 1 says:

[snip quote from standard]

> This has been discussed in the past on this list at length. Defining another
> std::swap for a particular type might seem to be a "specialization" at first
> glance, but it is actually an overloaded function, hence not legal.

The std::swap I have for my GMP mpz_t wrapper is like this:

namespace std
{
    template <>
    void swap(::Integer& a, ::Integer& b)
    {
        ::mpz_swap(a.mpz, b.mpz);
    }
}

This is a specialization, not an overload, and is legal.

> Here's a message from the middle of that old thread:
> <http://www.egroups.com/message/boost/6136>.

I've read this thread, and some others on a similar theme, but I don't
see anything contradicting the correctness of specializations like the
one shown above.  And I do find some like this:

   http://www.egroups.com/message/boost/2814

confirming that such specializations are legal.

> I decided to ignore this issue after adding swap to smart_ptr.hpp, and so
> the std::swap specializations/overloads (I still don't 100% understand
> which) are still there even though they are theoretically illegal.

Those are overloads, so they really are illegal.

Stephen