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From: "gccbugbjorn at fahller dot se" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/110828] union constexpr dtor not constexpr when used in
 member array
Date: Thu, 27 Jul 2023 16:25:19 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110828

--- Comment #2 from Bj=C3=B6rn Fahller <gccbugbjorn at fahller dot se> ---
If I write it in the same way in a function, it compiles.

consteval auto f()
{
    return S{}.f();
}

constexpr auto b =3D f();


However, if I break it into a constexpr object S s; and return s.f(), it do=
es
not compile, this time because the construction of 's' fails because it ref=
ers
to an unititialized variable, regardless of whether the member is an array =
or
not.

union type {
    constexpr type(){}
    constexpr ~type() {}
    int t;
};

struct S
{
    constexpr S() {}
    constexpr bool f() const { return true;}
    type v{};
};

consteval auto f()
{
    constexpr S s;
    return s.f();
}

constexpr auto b =3D f();

https://godbolt.org/z/68zY6ecxs=