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#include<type_traits>
#include<tuple>
#include<utility>
namespace dispatch
{
template<class,class>
struct acceptable;
template<class Abstract, class... Concrete>
struct visitor;
template<class Abstract, class Concrete, class... Concrete_Tail>
struct visitor<Abstract,Concrete,Concrete_Tail...>
: visitor<Abstract,Concrete_Tail...>
{
visitor() =default;
visitor(const visitor&) =default;
visitor& operator=(const visitor&) =default;
using visitor<Abstract,Concrete_Tail...>::visit;
virtual void visit(acceptable<Abstract,Concrete>&) =0;
protected:
~visitor(){}
};
template<class Abstract, class Concrete>
struct visitor<Abstract,Concrete>
{
visitor() =default;
visitor(const visitor&) =default;
visitor& operator=(const visitor&) =default;
virtual void visit(acceptable<Abstract,Concrete>&) =0;
protected:
virtual ~visitor(){}
};
template<class,class>
struct accept_type;
template<
class Abstract, class... Concrete,
class T
>
struct accept_type<visitor<Abstract,Concrete...>,T>
{ using type =acceptable<Abstract,T>; };
template<class>
struct concrete_type;
template<class Abstract, class... Concrete>
struct concrete_type<visitor<Abstract,Concrete...>>
{ using type =std::tuple<Concrete...>; };
template<class Abstract, class... Concrete>
struct accept_visitor
{
using visitor_type =visitor<Abstract,Concrete...>;
accept_visitor() =default;
accept_visitor(const accept_visitor&) =delete;
accept_visitor& operator=(const accept_visitor&) =delete;
virtual void accept(visitor_type&) =0;
virtual ~accept_visitor(){}
};
template<class Abstract, class Concrete>
struct acceptable : Abstract
{
void accept(typename Abstract::visitor_type& v)
{ v.visit(*this); }
};
template<
class To_Visit, class Visited, bool,
class Visitor, class Concrete,
class Fun
>
struct dispatcher : Visitor
{
dispatcher(const To_Visit& tv,const Visited& v, const Fun& f)
: to_visit(tv), visited(v), fun(f)
{}
dispatcher(const dispatcher&) =default;
dispatcher& operator=(const dispatcher&) =default;
using Visitor::visit;
protected:
~dispatcher(){}
const To_Visit& to_visit;
Visited visited;
Fun fun;
};
template<class Visitor, class To_Visit, class Visited, class Fun>
auto make_dispatcher(const To_Visit& to_visit, Visited&& visited, Fun&& fun)
{
return dispatcher<
To_Visit,Visited,
std::tuple_size<To_Visit>::value==std::tuple_size<Visited>::value,
Visitor,typename concrete_type<Visitor>::type,
Fun
>
(to_visit,std::forward<Visited>(visited), std::forward<Fun>(fun));
}
template<
class To_Visit, class Visited,
class Visitor, class T, class... Concrete,
class Fun
>
struct dispatcher<
To_Visit,Visited,false,
Visitor,std::tuple<T,Concrete...>,
Fun
>
: dispatcher<
To_Visit,Visited,false,
Visitor,std::tuple<Concrete...>,
Fun
>
{
private:
using base =dispatcher<
To_Visit,Visited,false,
Visitor,std::tuple<Concrete...>,
Fun
>;
public:
using base::base;
dispatcher(const dispatcher&) =default;
dispatcher& operator=(const dispatcher&) =default;
void operator()()
{ std::get<std::tuple_size<Visited>::value>(base::to_visit).accept(*this); }
using base::visit;
void visit(typename accept_type<Visitor,T>::type& data)
{
make_dispatcher<Visitor>(
base::to_visit,
std::tuple_cat<>(
base::visited,
std::tuple<T&>(static_cast<T&>(data))
),
base::fun
)();
}
protected:
~dispatcher(){}
};
template<
class To_Visit, class Visited,
class Abstract, class T, class... Concrete,
class Fun
>
struct dispatcher<
To_Visit,Visited,false,
visitor<Abstract,T,Concrete...>,std::tuple<T,Concrete...>,
Fun
>
: dispatcher<
To_Visit,Visited,false,
visitor<Abstract,T,Concrete...>,std::tuple<Concrete...>,
Fun
>
{
private:
using base =dispatcher<
To_Visit,Visited,false,
visitor<Abstract,T,Concrete...>,std::tuple<Concrete...>,
Fun
>;
public:
using base::base;
void operator()()
{ std::get<std::tuple_size<Visited>::value>(base::to_visit).accept(*this); }
using base::visit;
void visit(acceptable<Abstract,T>& data)
{
make_dispatcher<visitor<Abstract,T,Concrete...>>(
base::to_visit,
std::tuple_cat<>(
base::visited,
std::tuple<T&>(static_cast<T&>(data))
),
base::fun
)();
}
};
template<
class To_Visit, class Visited,
class Visitor, class Concrete,
class Fun
>
struct dispatcher<
To_Visit,Visited,true,
Visitor,Concrete,
Fun
>
{
dispatcher(const To_Visit& tv, const Visited& v, const Fun& f)
: to_visit(tv), visited(v), fun(f)
{}
void operator()()
{ apply(std::make_index_sequence<std::tuple_size<Visited>::value>()); }
private:
template<std::size_t... I>
void apply(std::index_sequence<I...>)
{ fun(std::get<I>(visited)...); }
const To_Visit& to_visit;
Visited visited;
Fun fun;
};
template<class Fun, class Abstract>
struct dispatchable
{
dispatchable() =default;
dispatchable(const dispatchable&) =default;
dispatchable& operator=(const dispatchable&) =default;
template<class... Arg>
void apply(Arg&&... arg)
{
auto t =std::forward_as_tuple(std::forward<Arg>(arg)...);
make_dispatcher
<typename Abstract::visitor_type>
(t,std::tuple<>(),*static_cast<Fun*>(this))();
}
protected:
~dispatchable(){}
};
}
#include<iostream>
struct chat;
struct chien;
struct animal
: dispatch::accept_visitor<animal,chat,chien>
{ };
struct chat
: dispatch::acceptable<animal,chat>
{ };
struct chien
: dispatch::acceptable<animal,chien>
{ };
struct attaquer : dispatch::dispatchable<attaquer,animal>
{
void operator()(chat&, chat&) const
{ std::cout << "griffe - griffe" << std::endl;}
void operator()(chat&, chien&) const
{ std::cout << "griffe - mord " << std::endl;}
void operator()(chien&, chat&) const
{ std::cout << "mord - griffe" << std::endl;}
void operator()(chien&, chien&) const
{ std::cout << "mord - mord " << std::endl;}
};
int main()
{
chat c1;
chien c2;
animal& a1 =c1;
animal& a2 =c2;
attaquer().apply(a1,a1);
attaquer().apply(a1,a2);
attaquer().apply(a2,a1);
attaquer().apply(a2,a2);
} |
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