CODEWITHSUNDEEP
c++clangc++14compiler-bug
Bulletmagnet
Bulletmagnet

Reputation: 6042

clang generates call to undefined function

The following code

#include <cstdint>
#include <array>
#include <utility>

std::size_t constexpr num = 5;

using Doubles = std::array<double, num>;

struct meow {

template<typename V>
static constexpr V value(V v, std::size_t)
{
    return v;
}

template<typename V, std::size_t... Indices>
static constexpr auto make(V v, std::index_sequence<Indices...>) -> std::array<V, sizeof...(Indices)>
{
    return {{value(v, Indices)...}};
}

Doubles doubles = make(3.1415926535897932384626433, std::make_index_sequence<num>());

};

int main()
{
    meow m;
    return m.doubles.size();
}

is compiled by GCC in a sensible fashion, but clang tries to call meow::make<double,0,1,2,3,4> without generating an implementation:

https://godbolt.org/z/9Mv67GeYW

What is going on? Did I get into IFNDR territory?

Upvotes: 5

Views: 252

Answers (1)

florestan
florestan

Reputation: 4655

I think this is a bug in clang, and it seems to be fixed in Clang 15.

This code seems to expose the same issue, warns in clang < 15 and not in clang >= 15.

class A {
  template <char N>
  struct Foo {
    static constexpr char Bar() { return 0; }
  };

  using Constants = Foo<1>;

  char var = Constants::Bar();
};

Upvotes: 3

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