CODEWITHSUNDEEP
c++visual-studio-2017c++17variadic-templatesfold-expression
Francis Cugler
Francis Cugler

Reputation: 7905

Variadic functions and fold expression: Fatal Error while trying to compile in Visual Studio 2017

I was reading this Q/A and some of the answers provided a possible solution for using Fold Expressions in C++17. I thought I'd try this technique within my own code.

This is what I have tried:

Some Header

#pragma once

#include <bitset>
#include <type_traits>

using Bit = std::bitset<1>;

template<typename... Bits>
typename std::enable_if<(std::is_same<Bits, Bit>::value && ...), Bit>::type
And(Bits... bits) {
    return (bits&...);
}

main.cpp

#include <iostream>
#include "Some Header"

int main()
{   
    Bit b1_0{0};
    Bit b1_1{1};
    Bit b2_0{0};
    Bit b2_1{1};

    // Intended uses:
    Bit res1 = And(b1_0, b1_1, b2_0); // res1 should = 0
    Bit res2 = And(b1_1, b2_1); // res2 should = 1

    std::cout << "res1 = " << res1.to_string() << '\n';
    std::cout << "res2 = " << res2.to_string() << '\n';

    return 0;
}

I'm using Visual Studio 2017; and this fails to compile I am getting a "fatal error C1001".

I don't know if it is coming from the fold expression or if how I am trying to apply the repeated & on each Bit that is passed into the function etc.

When I try this using Compiler Explorer: goldbot It compiles fine using either GCC or Clang but fails in Visual Studio...

How would I be able to do something similar to this that works in Visual Studio?

Upvotes: 1

Views: 210

Answers (1)

max66
max66

Reputation: 66200

Playing with goldbot seems that your code compile starting from MSVC v19.21.

I don't understand what wrong before; anyway, passing through a constexpr function as follows

template <typename ... Bits>
constexpr bool all_bits ()
{ return (std::is_same_v<Bits, Bit> && ...);  }

template<typename... Bits>
std::enable_if_t<all_bits<Bits...>(), Bit>
 And(Bits... bits) {
    return (bits & ...);
}

seems to works also with v19.20 and older versions.

Upvotes: 2

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