On Fri, May 16, 2008 at 12:45 PM, Marco Costalba <mcostalba@gmail.com> wrote:
On Fri, May 16, 2008 at 12:25 AM, Daniel Walker <daniel.j.walker@gmail.com> wrote:
If the overload_set were instead based on polymorphic_function, then after loading add_int for integers, you only need to specify plus once to handle all other types.
overload_set< mpl::vector<int(int,int), plus(_1,_1)>
add(add_ints, plus);
This is fundamentally different from writing overload_set< mpl::vector<"comma separated function signatures">
add(add_ints, plus)
In the latter case you instantiate plus for each signature in the overload_set (or multi signature function MSF, if you prefer). In your example you pass typename T where T = plus as template parameter. mpl::vector<int(int,int), plus(_1,_1)> Is no more a vector of signatures, it'a a vector of signatures + a class type. It is a vector of heterogeneous item types. This is _really_ totally different also from an implementation point of view. Indeed a MSF boils down to a hierarchy of operator=() each one defined on a given signature and each one forwarding to a corresponding boost::function What you suggest is to have a fall back MSF defined as: template<typename Signatures, class fall_back_poly_class> class function : public fall_back_poly_class { ......good old multi sig. function implementation ..... } In other words MSF _derives_ from poly class so that when a call matches some operator=() signature the normal path is choosen, when a call does not mach compiler synthetizes a new operator=() from the poly base class. Indeed Signatures can be more flexible of poly because poly is arity constrained, as example plus takes _only_ two arguments. While signatures list can contain signatures of any and also different arity. A simple generalization to overcome this could be: template<typename signatures_sequence, typename poly_sequence> class fallback_function : public "derive vertically from all the poly objects in poly_sequence" { ......good old multi sig. function implementation ..... } Is my interpretation correct? If it is and you are interested in such an object I think I can tweak multi-signature function to handle that. Thanks Marco