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From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Tue, 2 Apr 2024 18:01:56 +0100
Message-ID: <CAH6eHdQAbZLZWVzzs40vNBK7xJOwQMxvNbBcVpQaLPjbWcypKA@mail.gmail.com>
Subject: Re: [PATCH] libstdc++: Allow adjacent __maybe_present_t<false, ...>
 to overlap
To: Pilar Latiesa <pilarlatiesa@gmail.com>
Cc: ppalka@redhat.com, libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
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On Tue, 2 Apr 2024 at 18:00, Pilar Latiesa wrote:
>
> Just out of curiosity: would this also work?
>
> template<typename _Tp, typename _Disc>
> struct _Absent {};
>
> template<bool _Present, typename _Tp, typename _Disc = decltype([]{})>
> using __maybe_present_t = __conditional_t<_Present, _Tp, _Absent<_Tp, _Disc>>;
>
> That would avoid having to type 0, 1, ... manually.

This is subjectively horrible and, more objectively, would create
longer mangled names and additional RTTI.