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From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/95568] No CTAD with list initialization within
 requires-clause
Date: Thu, 18 Jun 2020 21:48:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95568

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
So far my guess is that this doesn't work because in a template
finish_decltype_type will create a DECLTYPE_TYPE in the deduction guide, so
we'll have

template<class T> X(decltype (X<T>::x))-> X<T>

deduction guide.  type_unification_real then tries to deduce T from a P/A p=
air
decltype (X<T>::x) and 0.  But:

The non-deduced contexts are:
-- The expression of a decltype-specifier.

and

If a template parameter is used only in non-deduced contexts and is not
explicitly specified, template argument deduction fails.=