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From: "gawain.bolton at free dot fr" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/105351] [concepts] Constraint checking does correctly match
 static member attributes
Date: Sat, 23 Apr 2022 07:22:22 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105351

--- Comment #2 from Gawain Bolton <gawain.bolton at free dot fr> ---
Yes I believe this is a bug and strangely enough clang also seems to have t=
his
issue.

>>From the draft C++20 standard concerning "simple requirements" (cf.
https://isocpp.org/files/papers/N4860.pdf page 109):

A simple-requirement asserts the validity of an expression. [Note: The
enclosing requires-expression will evaluate to false if substitution of
template arguments into the expression fails. The expression is an unevalua=
ted
operand (7.2). =E2=80=94 end note] [Example:
template<typename T> concept C =3D
requires (T a, T b) {
a + b; // C<T> is true if a + b is a valid expression
};
=E2=80=94 end example]

Clearly T::attr2 is not a valid expression for struct T { int attr2; }=