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From: "xmh970252187 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/69623] Invalid deduction of non-trailing template parameter
 pack
Date: Tue, 15 Mar 2022 01:59:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D69623

--- Comment #7 from jim x <xmh970252187 at gmail dot com> ---
In a simple way, the rule just requires that, for a function template, the
template parameter that is declared after a template parameter pack should
either appear in the parameter-declaration-clause before the template
pack(deducible) or just have a default argument.

````
auto f(auto..., auto a, auto...) { return a; }
````
IIUC, this is just disallowed since all arguments would only match the first
function parameter pack.=