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From: "daniel-dev at hotmail dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/110497] Wrong error on non-static data member referenced in
 concept definition
Date: Sun, 02 Jul 2023 08:08:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110497

--- Comment #2 from Daniel <daniel-dev at hotmail dot de> ---
Just some observations:

There was a similar discussion in

https://stackoverflow.com/questions/75443227/static-assert-on-an-ill-formed=
-no-diagnostic-required-expression


Note that if we use anything else which leads to the ill-formed expression =
for
T::b itself, e.g. B&, B*, int - gcc compiles without errors:

struct B {
    const bool b =3D true;
};

template <typename T>
concept C =3D T::b;

static_assert( !C<B*> );
static_assert( !C<B&> );
static_assert( !C<int> );

https://gcc.godbolt.org/z/9c6YW1vWe

I would expect (at least as a user) the same behaviour for static_assert(!C=
<B>)
too, in that case.

So gcc seems to consider T::b (with T=3Db) in this context as a well-formed
expression, but not a constant expression.

Looks strange.=