Variadic 模板在多个参数上给出错误

Question

我正在尝试来自 http://florianjw.de/en/variadic_templates.html 的代码：

#include <tuple>
#include <initializer_list>
#include <iostream>
#include <string>

template<typename Fun, typename...Ts>
void sequential_foreach(Fun f, const Ts&... args) {
  (void) std::initializer_list<int>{
    [&](const auto& arg){f(arg); return 0;}(args)...
  };
}

template<typename...Ts>
void print_all(std::ostream& stream, const Ts&... args) {
  sequential_foreach([&](const auto& arg){stream << arg;}, args...);
}

int main()
{
  std::string s1("string1");
  std::string s2("string2");
  print_all(std::cout, s1, s2);

  return 0;
}

但我收到以下错误：（当我将多个参数传递给 print_all 时）

main.cpp: In instantiation of ‘void sequential_foreach(Fun, const Ts& ...) [with Fun = print_all(std::ostream&, const Ts& ...) [with Ts = {std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >}; std::ostream = std::basic_ostream<char>]::<lambda(const auto:2&)>; Ts = {std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’:
main.cpp:14:67:   required from ‘void print_all(std::ostream&, const Ts& ...) [with Ts = {std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >}; std::ostream = std::basic_ostream<char>]’
main.cpp:21:30:   required from here
main.cpp:8:5: error: uninitialized const member ‘sequential_foreach(Fun, const Ts& ...) [with Fun = print_all(std::ostream&, const Ts& ...) [with Ts = {std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >}; std::ostream = std::basic_ostream<char>]::<lambda(const auto:2&)>; Ts = {std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >}]::<lambda(const auto:1&)>::<f capture>’
     [&](const auto& arg){f(arg); return 0;}(args)...
     ^

我做错了什么？ ideone link: https://ideone.com/

我尝试使用 ideone (gcc5.1 c++14) 和 Redhat 6 gcc version 4.9.1 20140922 (Red Hat 4.9.1-10)

Answer 1

由于 T.C. 尚未将此作为答案发布，所以我将其发布在这里，以便每个人都能找到它。

ideone link

#include <tuple>
#include <initializer_list>
#include <iostream>
#include <string>
#include <vector>

template<typename Fun, typename...Ts>
void sequential_foreach(Fun f, const Ts&... args) {
  auto fun = [&](const auto& arg){f(arg); return 0;};
  (void) std::initializer_list<int>{ fun(args)... };
}

template<typename...Ts>
void print_all(std::ostream& stream, const Ts&... args) {
  sequential_foreach(
      [&](const auto& arg){stream << arg;},
      args...
      );
}

int main()
{
  std::string s1("string1");
  std::string s2("string2");
  print_all(std::cout, s1, s2);

  return 0;
}

Variadic 模板在多个参数上给出错误

Variadic templates give errors on more than one parameter

c++

variadic-templates

c++11

c++14