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Subject: Re: std::string add nullptr attribute
From: Xi Ruoyao <xry111@xry111.site>
To: Jonathan Wakely <jwakely.gcc@gmail.com>, Jonny Grant <jg@jguk.org>
Cc: gcc-help <gcc-help@gcc.gnu.org>
Date: Fri, 10 Feb 2023 00:30:32 +0800
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On Thu, 2023-02-09 at 14:56 +0000, Jonathan Wakely via Gcc-help wrote:
> > Note, my code isn't like this, it is just an example to suggest
> > adding the nullptr attribute, as its clearly already rejected at
> > runtime.
>=20
> I assume you mean the nonnull attribute. That was added in 2020 and
> then reverted because it broke some things:

I remember I'd once made the same mistake when I suggested to add
nonnull for ostream::operator<<(const string &) and I was lectured:
nonnull is not only a diagnostic attribute, it also allows the compiler
to assume the parameter is never null and rendering std::string(nullptr)
an undefined behavior.

Then the example may just silently continue to run, instead of throwing
an exception.  It would be an ironic example: an attempt to improve
diagnostic finally made diagnostic more difficult.

--=20
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University