我已经从该站点找到以下代码，但是我无法适应我的目的：
我有用于创建具有可变变量的对象的工厂方法，并且具有函数“ apply”用于从工厂调用该方法并将其解压缩到以前保存到std :: tuple中的args中。
谢谢你的帮助 ！
#include <iostream>
#include <utility>
#include <iostream>
#include <functional>
#include <utility>
#include <tuple>
class A {
public:
A(int, int){}
};
class B : public A {
public:
B(int x, int y):A(x, y){}
};
template <class Base, class Derived>
class BaseFactory {
public:
template <class ...Args>
static Base* create(Args&&... args){
return new Derived(std::forward<Args>(args)...);
}
};
// ------------- UTILITY---------------
template<int...> struct index_tuple{};
template<int I, typename IndexTuple, typename... Types>
struct make_indexes_impl;
template<int I, int... Indexes, typename T, typename ... Types>
struct make_indexes_impl<I, index_tuple<Indexes...>, T, Types...> {
typedef typename make_indexes_impl<I + 1, index_tuple<Indexes..., I>, Types...>::type type;
};
template<int I, int... Indexes>
struct make_indexes_impl<I, index_tuple<Indexes...> > {
typedef index_tuple<Indexes...> type;
};
template<typename ... Types>
struct make_indexes : make_indexes_impl<0, index_tuple<>, Types...> {};
// ----------UNPACK TUPLE AND APPLY TO FUNCTION ---------
template<class Ret, class... Args, int... Indexes >
Ret apply_helper( Ret (*pf)(Args...), index_tuple< Indexes... >, std::tuple<Args...>&& tup){
return pf( std::forward<Args>( std::get<Indexes>(tup))... );
}
template<class Ret, class ... Args>
Ret apply(Ret (*pf)(Args...), const std::tuple<Args...>& tup){
return apply_helper(pf, typename make_indexes<Args...>::type(), std::tuple<Args...>(tup));
}
template<class Ret, class ... Args>
Ret apply(Ret (*pf)(Args...), std::tuple<Args...>&& tup){
return apply_helper(pf, typename make_indexes<Args...>::type(), std::forward<std::tuple<Args...>>(tup));
}
int main(){
// I got error: apply(<unresolved overloaded function type>, std::tuple<int, int>)
A* = apply(&BaseFactory<A, B>::create<int,int>, std::make_tuple(5, 25));
return 0;
}
...是的，我确实从编译器中读取了输出，但是如何获得代码的工作版本？
最佳答案
apply的功能类型不正确。应该是Args&&...（就像您在BaseFactory中一样），而不是Args...：
template<class Ret, class... Args, int... Indexes >
Ret apply_helper( Ret (*pf)(Args&&...), index_tuple< Indexes... >, std::tuple<Args...>&& tup){
// ^^
return pf( std::forward<Args>( std::get<Indexes>(tup))... );
}
template<class Ret, class ... Args>
Ret apply(Ret (*pf)(Args&&...), const std::tuple<Args...>& tup){
// ^^
return apply_helper(pf, typename make_indexes<Args...>::type(), std::tuple<Args...>(tup));
}
template<class Ret, class ... Args>
Ret apply(Ret (*pf)(Args&&...), std::tuple<Args...>&& tup){
// ^^
return apply_helper(pf, typename make_indexes<Args...>::type(), std::forward<std::tuple<Args...>>(tup));
}
int main(){
A* a = apply(&BaseFactory<A, B>::create<int,int>, std::make_tuple(5, 25));
return 0;
}
关于c++ - 我如何获得指向Factory::method(variadics…)的指针以进行延迟调用？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/29617318/