Re: Creating own Virtual method table
Christophe Meessen wrote:
I'm implementing a remote method invocation system. Each class has a
dispatch method whose role is to call the appropriate instance method.
The problem is that I need a generic member function pointer container
and a generic way to call the method by the dispatch method.
In my case all member functions involved have the same signature (same
arguments and same result value types) but the classes they belong to
may differ.
Apparently member function's type is bound to the class name. Is there a
way to get around this constrain ?
Yes, there are even libraries that help you do exactly that, e.g.
Boost.Function. If you have e.g. two classes Fou and Barre and their
according methods, you would have a common function signature:
typedef boost::function<int, double> function_type;
and you would then generate these functors using bind():
Fou object1;
function_type f1 = boost::bind( &Fou::method1, &object1, _1);
Barre object2;
function_type f2 = boost::bind( &Barre::method2 &object2, _1);
and store them in e.g. a map or vector.
The only solution I found so far is to encapsulate the method table into
a polymorphic dispatcher class with a virtual dispatch method. It is a
singleton and encapsulates all the type specific stuff. The class is
templated so that it is automatically generated for the appropriate type.
Nah, there is an easier way around:
You can wrap any memberfunction into a normal function:
// wrapper for Fou::method1
int fou_method1( Fou* o, double p1) {
return o->method1(p1);
}
Similarly, you can use a typeless pointer:
// wrapper for Fou::method1
int fou_method1( void* o, double p1) {
return static_cast<Fou*>(o)->method1(p1);
}
and then you have a function which has the same signature for any class,
provided the arguments match. Of course, this isn't type-safe due to the
typeless pointer, so you have to take care that this isn't used on the
wrong types.
Uli
--
Sator Laser GmbH
Gesch??ftsf??hrer: Michael W??hrmann, Amtsgericht Hamburg HR B62 932
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]