Hi Tobias, On 9/18/07, Tobias Schwinger <tschwinger@isonews2.com> wrote:
template<typename T1> static Base* object(detail::KeyRef nm, T1 a1)
This one will fail to compile with a non-copyable argument for 'a1' (unless 'T1' is specified explicitly to be a reference).
Yes, but something like static Base* object(detail::KeyRef nm, T1& a1) will fail with temporaries and something like static Base* object(detail::KeyRef nm, const T1& a1) will fail when c'tor arguments should be modified by the c'tor. I choose the first one because, as you noted, is the only one for whom exists a simple and 'intuitive' workaround for those (rare) cases: specify explicitly to be a reference. BTW, a little digression, if the standard would allow to elide argument passing for inline functions the real solution would be: template<typename T1> inline Base* shell(detail::KeyRef nm, T1 a1) { return object<T1>(nm, a1); } template<typename T1> Base * object<T1>(detail::KeyRef nm, traits<T1>::parameter a1); In this case the 'shell' is just a way to allow to typedef the type T inside a trait before to evaluate the argument and avoid the user to specify it explicitly...but unfortunately this does not work....I tried ;-)
Maybe you mean that 'boost::factory<a_concrete>' and 'boost::factory< another_concrete>'are distinct (even incompatible) types?
The clue is that both can be turned into objects of type 'boost::function<an_abstract*() >' to become polymorphic runtime entities.
I think your scheme will have troubles with multi argument support because you need to foreseen more abstract bases: an_abstract*(T1) an_abstract*(T1,T2) etc.. All with different types and this breaks single base polymorphic assumption -> you need one map for each argument arity. Perhaps for each argument arity _and_ types. Marco