为什么我不能将[]（auto &amp;&amp;…）{}转换为std :: function <void()> ？

Question

When I try to compile this:

#include <functional>

void f(std::function<void()> f)
{
}

void g()
{
  f([](auto&&...){});
}

on gcc 7.3, I get the following error:

[x86-64 gcc 7.3 #1] error: could not convert ' <lambda closure object>g()::<lambda(auto:1&&, ...)>{} ' from ' g()::<lambda(auto:1&&, ...)> ' to ' std::function<void()> '

Can someone explain why this is invalid c++? Or should I submit a bug report? (MSVC 14 accepts and compiles it to what I expect.)

Answer 1

This is a gcc bug . It interprets your lambda as follow:

[](auto&&, ...){}

So there's one argument, followed by C variadic.

If you add a name to your parameter pack, then it works as intended:

[](auto&&... pack){}