[pion-users] shared_ptr passed by ref, fails compilation under G++-6

[Robert L. <rob...@se...>]

hi everyone,

I had a look at this compilation error
(https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=811849), and 
managed to reduce the problem to a much smaller case:

----------------------------8<------------------------------
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/core/noncopyable.hpp>
#include <boost/function.hpp>

// fails to compile with g++-6 in a manner similar to
// https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=811849
// works with g++-5
class argument {
};

class test : private boost::noncopyable {
    public:
        void member(void);
        // note that the shared_ptr is passed by reference! is passing a
        // shared_ptr by reference even safe? it so, does it not need to
        // be
        // const?
        void callback(boost::shared_ptr<argument>& cb);
};

// but that this declaration is without the reference! putting it in
// makes it
// work in g++-6 as well, but see above about the question whether this
// is safe
typedef boost::function1<void, boost::shared_ptr<argument> >
callback_type;

void recipient(callback_type cb) {
}

void test::member(void)
{
        recipient(boost::bind(&test::callback, this, _1));

}

---------------------------->8------------------------------

to me it seems that the problem is that the shared_ptr is passed to the
callback by reference, which seems to be different from the callback
type expectations, and which sounds like a dangerous way to use a
shared_ptr anyway, at least to me. for kicks I modified finish_connection() 
in pion::tcp::server to take a non-reference argument, and that makes
this particular class compile with g++-6. 

there are similar cases in http::server which can be made to compile the
same way, but which also raises the question why this usage of a
shared_ptr is a problem for connection_ptr, but nor request_ptr.

there appear to be other compilation problems, but one at a time...

regards  robert

-- 
Robert Lemmen                               http://www.semistable.com