Re: [boost] [any] Multimethod for boost::any and modified boost::any to fit multi method

Subject: Re: [boost] [any] Multimethod for boost::any and modified boost::any to fit multi method
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2009-02-12 10:06:05

nowake_at_[hidden] wrote:

> I create multi method for boost::any using Modern C++ Design's
> multi method technique.
> 
> It can dispatch method dynamically like this:
> _________________________________________________________________________
> struct T1 {
>    string operator()(int value) const { return string("T1(int)"); };
>    string operator()(double value) const { return string("T1(double)"); };
>    string operator()(A value) const { return string("T1(A)"); };
> };
> // "entry" to Multi method
> bool t10(Multimethod::entry<any, any, T1, int>());
> bool t11(Multimethod::entry<any, any, T1, double>());
> bool t12(Multimethod::entry<any, any, T1, A>());
> 
> struct T2 {
>    string operator()(int value) const { return string("T2(int)"); };
> };
> // "entry" to Multi method
> bool t20(Multimethod::entry<any, any, T2, int>());
> 
> BOOST_AUTO_TEST_CASE(test04)
> {
>    any m((T1()));
>    any a(0);
>    BOOST_CHECK_EQUAL(
>          any_cast<string>(Multimethod::apply<any>(m, a)),
>          "T1(int)");
>    a = 0.0;
>    BOOST_CHECK_EQUAL(
>          any_cast<string>(Multimethod::apply<any>(m, a)),
>          "T1(double)");
>    a = A();
>    BOOST_CHECK_EQUAL(
>          any_cast<string>(Multimethod::apply<any>(m, a)),
>          "T1(A)");
> 
>    m = T2();
>    a = 0;
>    BOOST_CHECK_EQUAL(
>          any_cast<string>(Multimethod::apply<any>(m, a)),
>          "T2(int)");
> };

This looks overcomplicated.

A while ago, I offered something like this

any m = 0;
apply_visitor<int, double, A>(f, m);

or alternatively,
apply_visitor(f, m);  with f specifying all overloads in some 
compile-time reflection structure.

unfortunately, it cannot be made constant-time because std::type_info sucks.
Is your solution constant-time?