On Tue, May 13, 2008 at 9:32 PM, Giovanni Piero Deretta <gpderetta@gmail.com> wrote:
// adding all overloads, If I can get it my way :) struct foo_fwd { template<typename T> void operator()(T x) { foo(x); } };
my_msf f = foo_fwd(); //sizeof(f) = O( sizeof(boost::function) )
Comments? Did I convince you? ;)
Yes ;-) I'll stick to one_copy_only behaviour for set_all() But because to implement the N copy case is trivially simple (much simpler then your example) I would like to change the signature of set_all in the following way template<typename Fun> void set_all(Fun const& fun, bool multi_instance = false); Regarding the sizeof(f) == O( sizeof(boost::function) * N ) problem, given that - boost::function object are member data, so allocated on the stack - boost::function object are empty at instantation - boost::function object are created at MSF instantation (seldom event or not in critical loop context?), not during assignment (more often event, more performance critical ? ) I would like to know if - boost::function default c'tor does some allocation? An empty boost::function is cheap to create ? - When a functor is assigned by reference with boost::ref boost::function just copies a pointer/reference ? If the above it's true, but I am not an expert of boost::function, the problem of allocation of N boost::function perhaps is more theoretical then real, also the size problem, given that boost::function requires just 3 pointers does not seem a biggie IMHO. BTW remember the resul_of implementation request?
// a stateless polymorphic function object: struct twice { template<class Sig> struct result;
// the result type is simply the argument type, // but in principle it can be an // arbitrary function of the argument type. template<class T> struct result<twice(T)> { typedef T type; };
template<class T> T operator()(T f) { return f + f; } };
The bad news is that for a polymorphic function object implementation of struct resut is not trivial, MSF takes a sequence of signatures as template parameter! so implementing template<class T> struct result<msf(T)> { ????? }; for something like msf<mpl::vector<int(int), char(double, float), a_class(my_namespace::my_class), void(my_other_class, int, int, int)> does not seem immediate. The good news is that I've done it ;-) and the thing I'm proud of is that implementation does NOT require any metaprogramming stuff dealing with sequences and with building/splitting and comparing signatures and even does not require any argument-arity dependant new specializations apart from what is already present. So no new argument arity dependant code bloat!!! It is very simple, I even don't believe it can work...but it does :-) Marco