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From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/100976] [C++23] Make constexpr reference temp constexpr
Date: Thu, 01 Jul 2021 20:09:58 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100976

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Jason Merrill from comment #2)
> Or rather,
>=20
> int main()
> {
>   constexpr const int &r =3D 42;
>   static_assert(r =3D=3D 42); // { dg-bogus "" }
> }
>=20
> [expr.const]/4.7 says that "a temporary object of non-volatile
> const-qualified literal type whose lifetime is extended to that
> of a variable that is usable in constant expressions" is usable in a
> constant expression.

This was actually CWG 2126 which we don't seem to fully implement:

struct A { int n; };

const A &a =3D {1};              // const temporary
A &b =3D (A &)(const A &)A{1};   // const temporary
A &&c =3D (A &&)(const A &)A{1}; // const temporary

static_assert(a.n =3D=3D 1, "");
static_assert(b.n =3D=3D 1, "");
static_assert(c.n =3D=3D 1, "");=