[boost] shared_ptr overload ambiguous

From: Phillip Hellewell (sshock_at_[hidden])
Date: 2006-08-18 14:27:52

Hi,

When using overloaded functions with shared_ptr parameter, overload
resolution is often ambigous.  It is ambigous in situations where
using raw pointers would not be ambigous.

I've seen a few workarounds.  One workaround is to make one of the two
functions a template function, but that does not work in all cases.
Another workaround is to just give the functions different names, but
you can't do that when the function is a CTOR.

Well, to my surprise, I found a post from Artyom Borodkin from last
December that explains how it can be permanently fixed in boost
itself!  I thought there was no way I would ever resolve this.

http://listarchives.boost.org/Archives/boost/2005/12/97817.php

I went ahead and tested his suggestion by modifying the boost source
(I had to change slightly what he wrote), and it worked!

I changed this constructor:

    template<class Y>
    shared_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
    {
    }

to this:

    template<class Y>
    shared_ptr(shared_ptr<Y> const & r, typename enable_if<typename
is_convertible<Y*, T*>::type, void*>::type = 0): px(r.px), pn(r.pn) //
never throws
    {
    }

So to iterate what Artyom said, why would we not want to do this?!

Thanks,
Phillip Hellewell