The following code (a simplified example from a more complex code) fails to compile with gcc 11.3.0
#include <array>
#include <memory>
#include <tuple>
namespace tools {
template <typename U, typename W, std::size_t N>
void operator*=(std::array<U, N>& a, const W& b) {
for (auto& x : a)
x *= b;
}
}
namespace nameA {
template <typename Jclass>
struct Abase {
template <typename... U>
void calc(const typename Jclass::Utype& v, typename Jclass::Wtype& out, std::tuple<U...> par) const;
};
template <typename Jclass>
template <typename... U>
void Abase<Jclass>::calc(const typename Jclass::Utype& v, typename Jclass::Wtype& out, std::tuple<U...> par) const
{
std::unique_ptr<Jclass> j{new Jclass};
std::apply([&](auto&&...x) { return j->calc(v, out, x...); }, par);
}
}
template <std::size_t N, std::size_t M>
struct outtype {
std::array<int, N> a;
std::array<int, M> b;
private:
template <class F, class... ArgsType>
void doall(F&& f, ArgsType... args) { f(a, std::forward<ArgsType>(args)...); f(b, std::forward<ArgsType>(args)...); }
public:
void operator*=(int rhs) { doall([&](auto& el) { using tools::operator*=; el *= rhs; }); }
};
namespace nameA {
template <typename U, typename W>
struct Jbase {
using Utype = U;
using Wtype = W;
template <typename D>
void calc(const U& in, W& out, const D& d) const
{
f(in, out);
out *= d;
}
virtual void f(const U& in, W& out) const = 0;
};
}
struct J : public nameA::Jbase<std::array<int, 3>, outtype<3, 3>> {
virtual void f(const std::array<int, 3>& in, outtype<3, 3>& out) const { out.a = in; out.b = in; }
};
int main()
{
nameA::Abase<J> a;
std::array<int, 3> in = { 1, 2, 3 };
outtype<3, 3> out;
a.calc(in, out, std::make_tuple(4));
}
I compile the code with
g++ -Wall -pedantic -std=c++17 -o test test.cpp
and the error I get is
test.cpp:40:80: error: no match for ‘operator*=’ (operand types are ‘std::array<int, 3>’ and ‘int’)
40 | void operator*=(int rhs) { doall([&](auto& el) { using tools::operator*=; el *= rhs; }); }
The version of g++ is 11.3.0.
This seems very strange, because I explicitly have using tools::operator*=
in the lambda function passed to doall
. The compiler does not give a list of candidates for operator*=
either.
Link to godbolt where the code can be tested.
If I replace
void operator*=(int rhs) { doall([&](auto& el) { using tools::operator*=; el *= rhs; }); }
with
void operator*=(int rhs) { doall([&](auto& el) { tools::operator*=(el, rhs); }); }
then the code compiles with no warnings. I cannot see the difference between the two alternatives.
Also, with a newer gcc 13.1.1, the code compiles.
Is this a bug of gcc 11.3.0?
What you have observed is a gcc
bug which is confirmed here.