On Mon, Apr 7, 2008 at 2:46 PM, shunsuke <pstade.mb@gmail.com> wrote:
Eric Niebler wrote:
What I'm saying is that, in C++03, polymorphic function objects are broken, so we need the runtime equivalent of a metafunction class ... a generator for monomorphic function objects. Call it a function class:
struct fun_class { template<typename A> struct apply { typedef ... result_type; result_type operator()( typedef add_const_ref<A>::type a ) const { return ...; } }; };
Now both the return type calculation *and* the operator() have access to *all* the information about the arguments, even their lvalue/rvalue-ness.
After all, if you need "overload on rvalueness" in C++03, some workaround is needed.
BTW, this doesn't need a new concept: foo(i, boost::rval(3)); I don't like it of course, though. :-)
Good point and maybe this is what I didn't understand about using reference wrappers. In C++98 (and 03?), since rvalues and lvalues both bind to const refs, you can't really tell them apart without some convention (such as Shunsuke's above or reference wrappers) allowing/requiring the caller to specify which is intended. I don't see the motivation for Proto to attempt to distinguish rvalues and lvalues in C++03. Is there some dangling reference issue that I'm missing? BTW, Eric, congrats on Proto's acceptance! If I had written a review it would have been positive, but I've been out of it for many moons. ;-) Daniel