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From: "ppalka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/86439] CTAD with deleted copy constructor fails due to
 deduction-guide taking by value
Date: Tue, 22 Jun 2021 14:25:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D86439

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Another side effect of this is that GCC incorrectly rejects the following u=
se
of CTAD + braced-init-lists:

struct B { };
struct C { };

template<class T>
struct A {
  A(T, B);
};

template<class T>
A(T, C) -> A<T>;

A a(0, {});

The problem is that building the call to the deduction guide has the side
effect of changing the type of the {} to C, which causes later overload
resolution to fail because C isn't convertible to B.=