为什么这个变量不是在C++ 14的g ++中被推导为initializer_list？

Question

考虑下面的程序：

#include <iostream> 
int main() 
{ 
    int n = 3; 
    int fact = 1; 
    for(auto i{1};i<=n;i++) 
     fact*=i; 
    std::cout<<"fact of "<<n<<" is "<<fact; 
} 

它编译于ideone罚款，甚至当我使用-std=c++14选项。查看现场演示here。但是在C++ 14中，变量i应根据this推导为initializer_list。

没有为C++ 1Z的建议实现捆带初始化新类型推演规则：

For direct list-initialization:

1. For a braced-init-list with only a single element, auto deduction will deduce from that entry;

2. For a braced-init-list with more than one element, auto deduction will be ill-formed.

[Example:

auto x1 = { 1, 2 }; // decltype(x1) is std::initializer_list

auto x2 = { 1, 2.0 }; // error: cannot deduce element type

auto x3{ 1, 2 }; // error: not a single element

auto x4 = { 3 }; // decltype(x4) is std::initializer_list

auto x5{ 3 }; // decltype(x5) is int.

-- end example]

所以，规则改变了C++ 17。因此，当我使用-std=c++14时，程序不应该编译。 g ++中有这个bug吗？在C++ 14中，变量i不应该推导为initializer_list？

Answer 1

There is a proposal for C++1z that implements new type deduction rules for brace initialization

不完全是。如果按照链接到实际的纸张，有这么一句话：

Direction from EWG is that we consider this a defect in C++14.

这是足以让执行者也把它当作一个缺陷，并因此改变，即使在C++ 14模式下的编译器行为。