On Mon, 22 Nov 2004 12:54:17 -0800 "Robert Ramey" <ramey@rrsd.com> wrote:
I've never really understood this warning - basically it reminds me that I did what I intended to do.
Are you always sure? bool basic_iarchive_impl::track( basic_iarchive & ar, void * & t ){ object_id_type oid; load(ar, oid); // if its a reference to a old object if(object_id_type(object_id_vector.size()) > oid){ // we're done t = object_id_vector[oid].address; return false; } return true; } object_id_vector is a std::vector<>, so it has... reference operator[](size_type n), where size_type is "unsigned int" The line that generates the warning wants to convert a "object_id_type" to a "unsigned int" so it can pass the index to operator[](). However, object_id_type is a class (BOOST_STRONG_DEF) with the following conversion operators... operator T () const {return t; } \ operator T & () { return t; } \ where T is "unsigned int" So, in the attempt to convert from object_id_type to "unsigned int", we try both of the operators, and they both match. So, the compiler can not decide which one you want, because your object is non-const. Maybe in this situation, it does not matter, but there are many situations in which this multiple match can cause harm. So, I think the warnings should be eliminated, to prevent a piece of "bad" use from being overlooked because we get used to seeing these warnings. The presence of both operators in the BOOST_STRONG_DEF is what causes this ambiguity...