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From: "dangelog at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/102283] New: Inconsistent/wrong overload resolution when
 using an initializer list and a defaulted template parameter
Date: Fri, 10 Sep 2021 19:06:14 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102283

            Bug ID: 102283
           Summary: Inconsistent/wrong overload resolution when using an
                    initializer list and a defaulted template parameter
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dangelog at gmail dot com
  Target Milestone: ---

Hello,

The following testcase has an "inconsistent" overload resolution:


template <typename U>
struct helper {};

struct data {};

template <typename T, typename E>
struct S=20
{
    template <typename T2=3DT>
    void f(T2 &&); // #1

    template <typename E2=3DE>
    void f(const helper<E2> &); // #2
};

int main() {
    S<int, int> s1;
    S<data, int> s2;
    s1.f({});
    s2.f({});
}


https://gcc.godbolt.org/z/nsj48M7af


On GCC 11, the the first call to f() resolves to #1, but the second call
resolves to #2. I cannot find any reason for this inconsistency in the rank=
ing
of the overloads; no warnings are emitted under -Wall -Wextra.=20

Clang and MSVC both always call #1.=