相关疑难解决方法(0)

我正在尝试存储std::tuple不同数量的值,这些值稍后将用作调用与存储类型匹配的函数指针的参数.

我创建了一个简化的示例,显示了我正在努力解决的问题:

#include <iostream>
#include <tuple>

void f(int a, double b, void* c) {
  std::cout << a << ":" << b << ":" << c << std::endl;
}

template <typename ...Args>
struct save_it_for_later {
  std::tuple<Args...> params;
  void (*func)(Args...);

  void delayed_dispatch() {
     // How can I "unpack" params to call func?
     func(std::get<0>(params), std::get<1>(params), std::get<2>(params));
     // But I *really* don't want to write 20 versions of dispatch so I'd rather 
     // write something like:
     func(params...); // Not legal
  }
}; …

我两个月前发现了boost :: hana.看起来非常强大所以我决定看一看.从文档中我看到了这个例子:

std::string s;
hana::int_c<10>.times([&]{ s += "x"; });

这相当于:

s += "x"; s += "x"; ... s += "x"; // 10 times

我想知道是否有可能(如果是的话)写smthg:

std::string s;
std::array<int, 10> xs = {1, 3, 5, ...};
hana::int_c<10>.times([&](int i){ s += std::to_string(xs[i]) + ","; });

在编译时,甚至是一种"解包":

myfunction( hana::unpack<...>( xs ) );