On Sat, Jun 7, 2008 at 12:36 PM, Mathias Gaunard <mathias.gaunard@ens-lyon.org> wrote:
Giovanni Piero Deretta wrote:
I see two completely orthogonal fuctionalities here:
1- type erasure with multiple signatures of a single function object 2- aggregating different function objects in a single polymorphic function object *without* any type erasure at all.
That's what I've been saying for quite a while. MSF tries to do both, but should only provide the first.
The second should be another tool, like egg::overload. That kind of tool needs a lot of work alone.
I personally do not find egg::overload very satisfying. Lots of macros, separate type definition and usage... A solution like http://groups.google.com/group/comp.std.c++/msg/34b98493a8531d58 seems more elegant to me.
Ah yes! I already had that thread bookmarked :)
The problem being that it's not really possible, because the reflection mechanism used by function objects doesn't allow rewriting their signatures to forward to them.
Could you elaborate?
Ideally, a system that works even with polymorphic functions would be best, and if it doesn't require enumerating the signatures (they could be deduced) even better.
By the way, is it possible to deduce the constraints of an argument type and apply concept checking with SFINAE within a lambda expression DSEL?
For all operators that a DSEL implements, it already knows the required concepts (addable, dereferenciable, etc...), so it can remember every possible operation on every placeholder and carry it to the top level expression; then it can use sfinae on the union of all requirements of each placeholder. For more complex stuff (i.e. bind), it would be much harder: I have no idea if you can extract concepts from function signatures arguments as you can with types (at least without some kind registration). In C++ metaprogramming world, types are first class as you can have type variables (i.e. template type arguments), but I still can't see how you can store a concept in a (metaprogramming) variable. -- gpd