Re: [boost] [announce] Multi signature boost::function v1.0

From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2008-05-10 11:51:18

On Sat, May 10, 2008 at 10:32 AM, Marco Costalba <mcostalba_at_[hidden]> wrote:
> On Sat, May 10, 2008 at 3:17 AM, Giovanni Piero Deretta
>  <gpderetta_at_[hidden]> wrote:
>  >
>  > 1) can you dispatch on the dynamic type of an object? I.e.
>  >
>  > struct Base { virtual ~Base() {} };
>  >
>  > struct A : Base {};
>  > struct B : Base {};
>  >
>  > void foo1(A&);
>  > void foo2(B&);
>  >
>  > f = foo1;
>  > f = foo2;
>  >
>  > A a;
>  > B b;
>  > foo((Base&)a);  // calls foo1
>  > foo((Base&)b);  // calls foo2
>  >
>
>  Probably you mean
>
>  f((Base&)a);  // calls foo1
>  f((Base&)b);  // calls foo2
>
>
>  Anyway no you can't. But because also boost::function can't I fail to
>  see an inconsistency. Indeed
>
>  boost::function<int(A&)> f= foo1;
>
>  f((Base&)a);  // calls foo1  <---- COMPILER ERROR: cannot convert
>  parameter 1 from Base to A&
>

Ok. I know that boost function can't do it, but I thought that dynamic
dispatching
would come easier once you  had multiple overload dispatching
functionality. Thinking
of it, it probably needs registering all derived types of Base.

Anyways I do not think that MSF should provide this, it was just a whish :)

>
>
>  >
>  > 2) If I have a polymorphic function object, can I store a single
>  > instance of this object
>  > and specify multiple signatures? i.e.
>  >
>  > struct foo_t { template<class T> void(T){...} } foo;
>  >
>
>  Sorry but the line
>
>
>  struct foo_t { template<class T> void(T){} } foo;
>
>  does not compile for me. Probably I'm missing something obvious.
>

I'll reply to this in another email.

-- 
gpd