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From: "bisqwit at iki dot fi" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/94128] ICE on C++20 "requires requires" with lambda
Date: Wed, 11 Mar 2020 09:42:31 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94128

--- Comment #2 from Joel Yliluoma <bisqwit at iki dot fi> ---
Yes, it is valid.

=E2=80=94 The auto parameter is valid since C++20. It is called a =E2=80=9C=
placeholder type=E2=80=9D,
which has existed since C++11. C++20 made it valid also in function paramet=
ers.

=E2=80=94 The =E2=80=9Crequires=E2=80=9D is a valid keyword since C++20. It=
 specifies constraints that
the parameter must match. The double =E2=80=9Crequires=E2=80=9D manifests i=
n certain
situations.

=E2=80=94 Until C++20, lambdas were not permitted in unevaluated contexts. =
Changed in
C++20.=